They also talked a bit about new native compilation for .net (C# initially), and it uses the C++ compiler back-end, so it gets many of the spiffy optimizations like automatic vectorization/parallelization of loops and such. I think that won't be released until near the middle or end of next year, but its a promising avenue to tighten the performance gap with C++. The design and semantics of C# require a more heavy-weight runtime than C++ requires, so you won't see complete performance parity, but its good news still. They also made passing mention of looking at ways to make accessing native libraries (like, say, DirectX) from natively-compiled .net programs less costly, so that would be grand too. It'd be great if p/Invoke et. al. could be mostly collapsed away.

XNA is dead, but one can dream of a successor to XNA based on native compilation, and a programming environment that takes full advantage of what Roslyn provides for productivity and machine-directed code assistance. Roslyn gives you "simple" things like rock-solid refactoring and code transforms, but its also my understanding that a platform like XNA could be Roslyn-enhanced so that it could actually suggest better use of the library for your code. That would be pretty amazing.

That question is basically the same as "what will replace XBLIG on Xbone" (the marketplace for selling XNA games, as opposed to licensed games).
On 360, big publishers could put games on XBLA, and hobbiests/XNA-users could put games on XBLIG.
Licensed developers (non-XNA games) had to sell their soul to a big publisher to get onto XBLA, and hobbiests were segregated into the separate XBLIG ghetto...

On Xbone, there is no hobbiest option yet, only licensed developers can get on there. However, it's no longer restricted to just the big publishers, so indie devs can sell their games on there directly, without being robbed by a publisher... That's already a huge positive change for the indie scene.

So:
• big publishers - still sell their own games just the same, but are no longer given a free pass to exploit indies.
• indies (licensed) - can actually get onto the xbox live store now!!
• hobbyists (unlicensed) - completely excluded, for now.

They've said that they don't want to create a segregated store, with the XBLA/XBLIG schism that the 360 has... So that means they want all developers to be licensed. They can make this easier for hobbiests to get on there by waiving he licensing fees, and letting people use retail Xbone kits as dev-kits... But shipping a licensed console game requires that you comply with about 50 pages of QA/TCR/TRC checklists, and doing the QA work to ensure your game is compliant will always cost about $10k... So unless MS gets rid of the compliance testing, hobbiests will continue to be excluded. The only way I can imagine that they would to this, is to create a segregated store, where licensed titles are on XBLA, and unlicensed/non-compliance-checked titles are in the XBLIG ghetto... So we'll have to see if they reverse their stance on that.

C# is great for productivity, and Roslyn promises even more. Its true that C++ will probably never be as easy or fast to write as C# -- that's the price you pay for taking tighter control of how your program executes -- but its also worth noting that modern, idiomatic C++ (C++11 and upcoming C++14) style is not your grandfather's C++ -- its easier to read, write, and reason about and it requires a lot less code to do the same things you're used to without sacrificing its speed or flexibility. Done right, its much less scary or difficult than its ever been before.

But the most important thing is for you to use what you find productive and which gets the job done.