I don't have any inside information, this is just some guessing from someone who knows a lot about programming:
I seem to remember someone (IG?) saying the update was 70% or 80% (or some other number in that range) finished. Now take that percentage with a grain of salt because often the last 20% of the work take 80% of the time in programming (and it is not clear whether that purported percentage was about code or time). So, assuming IronGalaxy was working on the update for a year it could take them another 4 months or another year. A different developer unfamiliar with the code would need to add maybe another 2 months.
Usually most debugging is done last so just dumping this update to users would be not useful at all, likely a lot of systems don't even run and secfault immediately. Also the time for debugging is always underestimated. If IG really did an accurate estimation of the needed time they would be one of a rare breed of game developers.
One of the most critized bugs is the Xbox save bug. I don't think TFP could release an update without fixing that bug. But it is not at all clear if that is even possible without rewriting the file handling subsystem. It isn't even clear if that might need more resources like RAM and because RAM is already scarce would need even more changes and possibly might make it impossible. There is also a rule from MS and Sony that savegames must be (backwards or both ways?) compatible, is it even possible to solve the issue and follow that rule? I don't know, I can only say there is a chance this alone prevents any thought about an update.
Ok, I'm a pessimist. But I'm 99% sure just releasing what is there is impossible. And developing a version that TFP could release without getting flak from all sides and more importantly that would go through the quality check at Microsoft and Sony might take from 4 to 18 months (best to worst)