Sorry. I don't really understand that. A computer can be both client and server depending what software I run on it. Do you mean there are different versions of Windows called 'client' and 'server' and the certification requirement of 'cannot switch off restricted boot' only applies to the 'client' version?
Can't you run server software on 'Windows client'? How do they stop that happening? (can you tell I've not taken much notice of Windows for a really long time now)
Presumably they will want Windows to run on ARM server kit so there will be a version of 'Windows server' for ARM soon enough. If that won't have the 'you can't turn off resitricted boot' antifeature certification requirement then thats good.