I'm kinda torn really.
On one hand, there's a lot of talent on the NXT roster and that talent has been used extremely well by some extremely concise, consistent booking. As a result, I think it's natural as a fan, downright instinctive really, to want to see some of that talent showcased at the biggest show of the year.
On the other hand, I also like the idea of NXT being pretty damn close to being an autonomous, separate entity from the main roster. There's been little crossover between the developmental and main rosters aside from the occasional uses of mid-card to lower mid-card wrestlers from the main roster. That minimal crossover coupled with the talent, the different production values and strong booking does make NXT come off as an alternative to the more "mainstream" WWE product.
IF NXT becomes it's own separate touring brand, which is said to be a goal Triple H hopes to reach in 2016, then MAYBE I could see NXT getting to be not only a part, but maybe a significant part of WrestleMania in 2017. Things are starting to look good for the WWE Network and if WWE is able to eventually get 2-3 million regular subscribers, then there's little doubt that NXT could be the centerpiece show for the network. If NXT is able to be a successful touring brand, even filming episodes of the televised program in different arenas, then I could POSSIBLY see NXT being branded as more of an equal to the main roster. After all, while NXT is the name of the TV show, it's also the name of the developmental territory itself and wrestlers don't make it to the NXT TV show without first showing what they've got during actual training sessions.
However, there's still a lot of work to do and the results of said work won't be revealed until pretty far down the line. Until/unless NXT becomes successful enough to be viewed as sort of its own legit brand, it's still the "minor leagues" in some ways. If NXT did run a match on the WrestleMania card, I probably wouldn't be against it, but the match itself, the wrestlers competing in it, whether they got any significant time on WWE television to promote the match, the story behind it, etc. would show if there's any real payoff. I don't see a point in just slapping together a 5 or 10 minute match onto the WrestleMania card just for the novelty of it being a match of NXT wrestlers. If it's on the card, then treat it like it has meaning.
Oh and probably the most important thing, I think they'd need to let Triple H & his team book it. Triple H would need to convince Vince, get on his hands & knees if he had to, to let his guys book the NXT match & storyline. Threaten to sic Stephanie on him, threaten to tell his mother, and yes she's still alive btw, or whatever. I don't have faith in the stability of Vince's booking these days. I'd rather the match not happen whatsoever any day than for Vince to screw it all up just because he thinks he knows better than everyone else around him.