This arguement concerning Muay Thai and Shanshou have become quite heated which is normally the case when styles mixes with nationalistic pride are involved. I would like to share my humble opinion in the assessment of the subject concerned.
Let us start by looking at the historical development of both the fighting system .
We start with Muay Thai first. Muay Thai shares similar fighting tradition as that of Burma, cambodia and Laos. These were Indianised Kingdoms with strong influences from Hindhuism in their arts and crafts, philosophies, religion(subsequently converted to Therevada Buddhism) and system of Government. They shared similar fighting skill as oppose to that of Vietnam which was mainly Chinese based.
Before 1930s skill level among these countries were more or less equal. However the adoption of western safety rules such as the ring, gloves, weight division and rounds pushed Thai standard far above that of others. With all the safety rules in placed more professional participation was made possible which resulted in a boomed industry for many to earn a living. With more competition, skill level moved up dramatically. This was particularly so when western boxing was adopted and it let to improved skill in punching and guarding. No nation on earth in recent history has such wide spread experience like the Thais in sport of all round full contact fighting. The fighting skill has improved and transformed over the years. It is without exagerration to say that every Muay Thai technique works as the techniques were borned out of countless ring fight experiences over the years. The change in level of skill can be seen in old photographs, film footage and old fight manuals.
The other nations tried to copy the same safety measures which led to this boomed industry but with limited success due to colonialism, wars and in recent years socialism or communism which banned or strongly discouraged fighting sports.
Its was without valid reason for the Cambodian to claim Muay is theirs as the Khemers kingdom were older and they are indigenious in this part of the world. The Thai were relatively new comer from Southern China. But who actually developed it? Muay Thai is undisputely Thai as it is a product of Thai efforts, Thai experience,Thai development and Thai genius. I agreed that given the same environmnt the same mentioned nations could have developed their Muay to the same standard as the Thai but this did not happened and Muay Thai SHOULD remain Thai.

Now let us move to the historical development of Chinese Martial Arts. In mid 17th Century China was conquered and ruled by the Manchu(Qing dynasty), a foreign race, for more than 200 years until early 20th century. The Manchu, who were in minority that constituted less than 3% of the total population, instituted a policies of suppressing martial arts practices by encouraging the artistic element instesds of the fighting elements of the arts. Martial arts practices were generally discouraged or banned on certain periods. This is to preserve their position as the ruler by supressing militant spirit of the Han Chinese for fear of rebellion. During this period we saw a big decline in the effectiveness of Chinese Martial Arts as a fighting arts in the general population. Fortunately, the Triad,which was formed to overthrow the Manchu,was able to preserve fighting aspect of the arts among the small pool of its members.
During the Nationalistic period(1911-1949) Chinese Martial Arts enjoyed a brief revival but was surpressed again when the communists took over in 1949. From 1949 to early 1980 fighting sports including boxing were banned. It only started to liberalise in early 80s as China gratually opened its door to the outside world and influences.
Since the liberalisation, fighting aspect of Chinese Martial Arts (shanshou/Shanda) has picked up at an amazing rate. These are my personal encounters.
In late 1980s China only took part in form (pattern) events in the World Wu Shu meet. They did not participate in Sanda(Lei Tai) event as they were not readied.
In 1991 during my long travel in China,I trainned a grouped of young villages in Muay Thai for two months before putted them against the best Sanda group from nearby town. With only two months training ( two and a half hours, 7 day week)we still able to emerge as winner with 3 wins and 2 lost.
In end 1993 I was again in China trying to arrange an International mixed Martial Arts tournament but unable to recruit fighters due to lack of response.The point I am trying to make here is the general low standard in China then.
In around 10 years, the standard has risen to such that they were able to beat Korean, Japanese, American (3 times)and Thai was beyond my belief. Never mind the judges were biased and the rules favoured them. To me the Chinese fighters being able to survive first few rounds without being knocked out by top rated Thai had far exceeded my expectation. This time round in Kings Birthday, I know the Thai will pit their best to reclaim Muay Thai's supremacy as an all round full contact fighting sport. I actually expected all five KO with some in the early rounds but that did not happened. We have to give credit to them, as in such a short space of time they have come a long way.
As a comparison the west started doing Kickboxing in the late 60s and early 70s. With the benefit of the their own indigenious boxing skill, not many western fighters, with exception of VERY selected FEW, able to handle 2nd rated or 3rd rated Thai fighters in early 80s. I remember during that period a few Cambodian refugees who was unrated in Thailand was able to dominate national titles as well as European title in Europe. Many of so called world champoins in US lost to low rated Thai and some western "legend" refused to fight in Thailand when invited. Today of course is a different picture . The west has come a long way with more experience and better exposore over the years. Some of the top fighters are able to face the Thai toe to toe without being intimidated.

In conclusion where do we go from here with the Chinese Sanda. As at now their standard still fall short when comparing to top Muay Thai fighters, Thai as well as non-Thai. But we know that they will developed in an amazing pace like most things the Chinese do today. I believe they will provide a credible competition in not too distance a future. I believe competition will help to push up overall standard and in addition it adds more variety and excitement to the full contact fight scene. With these I would like to say WELCOME!