WI: A modernized Qing China, impact on the World Wars and co

If we put a butterfly net on things until WWI, and make Cixi align with the CP, sure, a modernized China with modernized ground forces would be an asset for the CP and a detriment occupying too much Russian and Japanese attention, but likely wouldn't cause an Entente coalition collapse as early as 1914.    Japan would not be a vital center for the Entente coalition, and China would be unlikely to have fleet superiority to mount an invasion or take the naval initiative. And while Russia could lose some borderlands in Asia, it had few vital centers of gravity in Asia. Depending on Chinese spheres of influence, there could be a "Silk Road" of supply for the CP though passing through some still independent Central Asian Khanates like Bukhara and Khiva and Persia, for communication between western China and the Ottoman Empire and thence to the European members of the CP.

A China modernizing like Japan during the Dowager's reign may have been wracked by by mid-century rebellions and humiliated by the two opium wars, but would not have suffered the late 19th century humiliations like the Sino-French War of the 1880s, the Sino-Japanese War of the 1890s, the German and other European concession grabs at Qingdao and other places of 1897-98 or the Boxer Rebellion and suppression of 1900-1901, or the Russo-Japanese War being fought on its soil, or probably even Korea's.  So that is a set of substantial differences.

In terms of effect on WWI, yes, a drain on Russia, which should wear out its endurance faster. China would also be the main target of Japanese effort, which would wear down both of those countries energy - Japan's main secure gain I would expect to be German Micronesian islands.  

China would be a threat to western concessions in Hong Kong and Shanghai and other treaty ports set up in the opium wars, with the Japanese likely leading their defense but with British and French support, and maybe the Chinese and the Entente being circumspect around the ones where the Americans operated.

I anticipate trouble between China's Vietnam/Annam proxy and its border with France's Cochinchina and Cambodia protectorates, with Siam being more likely to be China and CP aligned, and possibly a Chinese backed Upper Burma still being around, clashing with British Raj forces in Assam and Lower Burma.  

China's urban economy should be hammered by naval inferiority and blockade.

If the Entente nevertheless sticks it out and wins, likely requiring US help, China may be an ultimately undefeated member of the CPs, or it could get off relatively lightly, merely being forced to grant self-determination and yield special suzerainty claims over Kingdoms, Empires or Republics or "Mandates" in Korea, Indochina, Upper Burma.  Or, despite China being miles better off than OTL, with higher expectations, being on the losing side of a world war may still be such a shock that defeat causes regime change, with Chinese revolutionaries taking the end of the war as a great occasion to end Manchu dynastic rule and proclaim Han rule and probably republicanism.  [An odd thought - If, like in our world, the Entente still wins, but the Russians fall before that happens, the Chinese Republic and sphere of influence vis-a-vis Bolshevik Russia may be OK - like China still controls Mongolia, Tannu Tuva, and Xinjiang, and maybe even some of southeastern Central Asia, but Japan gets a "League of Nations Mandate for Korea", Britain gets a "Mandate" for Upper Burma, France gets a "Mandate" for Laos - it could spend very little effort in the area, and the USA, with forces based out of the Philippines, gets a "Mandate" for Annam and Tonkin (all Vietnam except the French far south), that hopefully it can complete without too much mess between the 1920s and 1940s.