There will be a patch associated with Nemesis. Can't comment on what is fixed/isn't fixed/included at this point in time, however, there are at least some bug fixes included.
Well, its good to know that there will be a patch, although (as others have said) its a bit frustrating to be left in the dark on whether fairly major bugs have been fixed yet. [I get it that you aren't at liberty to say it yet.]
The bug that I cited for example: Galactic Law is a major feature of the free patch that came out alongside federation, and particularly impactive galactic laws that would place many empires in breach were a major features of the paid Federation DLC (such as Renegade Containment Doctrine, Universal Prosperity Mandate, etc.), as well as of course other stuff like the Juggernauts. The probably is that with the current bug with galactic law, being in breach of galactic law DOES ABSOLUTELY NOTHING - even if you violate the conditions, you don't actually go into breach like you are supposed to and you don't get hit with the penalties/sanctions that you are supposed to. I reported this back when 2.8 came out, and was really hoping that we'd get a 2.8.2 patch to correct is, as a major part of the Federations DLC now does not work as advertised (because that part doesn't work at all). But as that 2.8.2 never came out, this feature has been broken for months now. That's why I'm so keen on hearing on whether this is fixed in 2.9/Nemesis or not - its quite off-putting to have my resolutions not work correctly, especially when I'm quite a fan of trying to use the 4th tier egalitarian resolution to penalize slavers, and overall demotivating.
I'd feel a lot better about Nemesis and getting it if I confidently knew that this issue had been fixed in the patch.
(There are a bunch of minor things that would also be on my wishlist, like the democracy leader bug being re-fixed after years, but the galactic law breach working again is the thing I'm really concerned about.)
Well, to be more positive on the end note, what you guys have teased on the opposite of the Nemesis (the Custodian referred to in the blurb) sounds really interesting and potentially highly aligned with my play styles, so IF (and that's a key if) the major bugs are fixed Nemesis could be an immediate buy.
EDIT: Also, I already have filed a bug report about the galactic law issue, months ago back in the 2.8.1 days I think.