Aurora R6, upgrading motherboard for i9-10850k

The other issue you will face is if you have the base OEM 460W PSU in your Aurora R5 you would need to upgrade that to support a 10850k.

"R11 motherboard form factor appears similar to R6."

I thought the question is about an aftermarket motherboard, not an R11.  I think he meant "Z series" not R series as in R11.  Since you can't really find the R11 motherboard by itself for sale anywhere.

Edit: But yeah, I was confused about the "R series" too when I read it.

Re: the oem motherboard's IO shield is fused to the metal chassis

Dell makes sure R5-8 cases are only upgradable within Alienware Aurora R5-8 class.

IO shield appears to have same layout among R5, R6, R7, R8, and even R9, but not R11 or R10.

R5

R6

R7

R8

compare to

R9

R11

R10

so I don't think I'll be able to upgrade my motherboard but my CPU needs an upgrade still so do you know the best CPU I might be able to get for it

To upgrade your CPU to a 7700k from a non-K CPU,you will also need the liquid cooler, and VRM heatsink.  The 850w PSU option is either highly recommended or required depending in your GPU.

New generic cases with clear side view panel are not expensive. 
Perhaps OP wants to hold on to an Alienware case because of certain personal preference.

@r72019 FWIW, my initial impression when R5 released was the rear I/O needed cut / Dremel-tooled out ... a few months ago I read that an owner who modded the case said he 'drilled out the rivets' to remove rear I/O shield. If so, then that'd be a better & a cleaner removal method than cutting it out, where 'explore drilling out the rivets if it's possible to, before you explore cutting out rear I/O plate' may be best advice for that mod (=

Re: an outdated Aurora R6 chassis

most people could not tell the difference between older R6 and slightly newer R8 case.  A casual observer could not tell second gen triad case of R5 from 1st gen R2 either.  Every case style becomes outdated after a couple of years.  How long would R9-11 case last?
While the ubiquitous modern case with clear side view is still in vogue now, it will be on the wane tomorrow.  Some builders may prefer to hold on to a classic fully upgradable case only upgrading components.  Full tower cases such as XPS730(x), Area 51 Phobos (R1) still have their cult followers.  In comparison R5-8 cases are difficult to upgrade.  The triad case is either adored or eyed askance.