For me the game gets the pacing just about right for some side quests to be done in between main quests. Geralt still has a life, after all, and the time he's been looking for Ciri is implied to be long. Hell, the game starts with Geralt and Vesemir discussing Ciri while taking on a Griffin contract.
Some main quests feel more urgent than others, but I thought the game offered moments of relative calm often enough to let the player do side quests guilt-free. But there are so many side quests, so many witcher contracts, so many of those bloody interrogation marks that there's just no way to tackle all of it without feeling like you're running counter to Geralt's alleged priorities. So an immersive epilogue to the main quest becomes essential to wrap the game up satisfyingly.
As I said before, I think the perfect way to do it -- on top of the list of changes that is being regularly requoted here and that I'll requote below -- is to have a final main quest that officially ends the playthrough. Did you end up with Triss in Kovir? Then the final main quest is to meet Triss and go to Kovir when you feel ready to move on. She can be waiting somewhere for you. If you ended up alone, but with Ciri as a witcher, the final main quest could be to go on the path with her (in a cutscene, not in gameplay, although a final little quest with Ciri would be nice). If both outcomes -- Ciri as a witcher and Triss going with you to Kovir -- happen together, the final main quest could be to train Ciri then go to Kovir with Triss, in which case you would meet both characters together. All of these outcomes would have a final cutscene just to wrap things up (in the latter outcome, for example, the characters would establish that Geralt would go on the path one last time with Ciri, then leave with Triss to Kovir). The end. Roll credits.
With that said, here is, once more, the list of changes that is being requoted as a nice basic template for an epilogue.
and go do some contracts with Ciri. 
