I don't think there's going to be some new technique that breaks Yoshi's potential open. The options in the game just aren't there.
However, I think Yoshis can do a lot of work in refining their play and really breaking down match ups. Regrettably, since most Smash discussion now occurs on Facebook, Twitter, or Discord, there is no well structured, centralized location for discussion and real analysis. People generally do not seem interested in this type of interaction anymore, and so metas stagnate. And this isn't just true for Yoshi -- many character boards are dead, with stagnated metas.
The only thing keeping the meta developing are the tippy top players that are consistently topping events and taking names. But their progress is individual and does not contribute to a character's meta -- no techniques are shared, and the general playerbase does not improve as a result of their breakthroughs.
I won't ever expect any project like Brawl's match up chart to happen again. That project was a huge collaboration that saw participation of players from nearly every character, contained at least a month of consistent discussion, and led to actual analysis of matchups from both sides of the equation. That just...won't happen now. There's no tangible reward for doing that. No sponsors, no Twitter glory, no reception of a higher seed at a tournament. So the boards die, players make progress in isolation, and metas stagnate.
On the whole, the playerbase of Smash 4 will remain less capable and skilled than the playerbase of Brawl. Nobody cares to improve the outlook of the lower leveled players anymore.