If you go SRAM 1×11 then you’ll need a new freehub. If you’re just going for XTR 1×11 then a standard 10 speed freehub will do the job.
If you’re so inclined, you can of course mix XX1 and XTR by using XTR shifters and mech with an XX1 cassette for the wider gear range. I’m not sure if you can use XX1 shifters and mech with an XTR cassette but I can’t see any reason why it wouldn’t work.
You could try 1×10 with a new cassette and an extender cog along with a thick/thin chainring and it would work out a lot cheaper than an 11 speed set-up but I’ve no idea how well it works.