I could see another of Yoda's species, perhaps a young one coming from the woodwork... Be like hi I am Yoda's apprentice... Wait what?!?!?! Yeah he trained me like 200 years ago, I just woke up from a nap where is he?

Yoda's son, with Yaddle........

But in all seriousness, i like the first-half of your idea.

Rather than doing a Yoda origin story, bring in a 3 meter non wrinkly talks somewhat straighter than Yoda version? Give him a cool name make him apprentice to Ben Skywalker? WHat?!?

As far as in concerned, the writers can include a force ghost Yoda if it actually serves a real purpose to advance the story along as opposed to using him to get some cheap fanboy appeasment. The operative word to be used for this trilogy hopefully is intentionality or purposefully driven decision making as opposed to doing things on a whim because it caters to what the hardcore star wars audience may like to see or at least "think" they would like to see on film.

Force ghost Yoda duels the evil ghost of Sidious??? NOW THAT'S WHAT I'M TALKING ABOUT.

I

I will pass on this altogether the more I think about it.

How about Qui-Gon along with Yoda, Obi-Wan, and Anakin?

If they have to bring back the Sith...