The funny thing is, with the timeline/ages involved
and knowing what we now know about Grogu's past, and where he spent time, that everyone has spent over a year calling him "baby Yoda" might prove to be more accurate that we realized.
Think about it.
He came from
somewhere.
50 years ago, Yoda might've had a drunken one-nighter with Yaddle.
Don't laugh...crazier things have happened.
Maybe the reason he was hidden away is because the involved parties (librarian lady, Bail Organa, Obi-Wan, Yoda himself, etc.?) knew his lineage/capabilities and realized he could not fall into enemy hands. "Away from here, get this child, you must!"
Ahsoka said herself she'd only ever seen another being like this, mentioning Yoda by name.
I think there's more to Grogu than we know, and things will slowly spill out in episodes (or seasons?) to come.
If they try to drag Luke into this show, they've got their work cut out for them because Mark Hamill looks like the side of a post-hurricane tool shed, or the south end of a mule walking north. God help them. There's only so much CGI in the world, people.
But, as I've mentioned before, blue, grainy/scan-lined flickering translucency (hologram) can hide a multitude of sins. So that, along with a strategically placed hood/shadows, perhaps some obscuring facial hair and a bit CGI de-aging work could give us a few seconds of Luke Skywalker, circa 9 ABY? They gave him the Chuck Norris hair/beard look, trying to make him appear younger, for a few scenes in
The Last Jedi, so they've already gone down that road with the character already (trying to present a Luke Skywalker as he appeared in the time between ROTJ and TFA/TLJ.
*shrug*
But, I could actually buy Force ghost Obi-Wan - Ewan McGregor - a bit easier. At one point I would've said they'd have to age him to Alec Guinness levels for it to make sense, but, as Lucas' tweaked OT shows, Force ghosts don't always appear as you'd expect. Originally we saw British actor Sebastian Shaw appearing as a Force ghost next to Obi-Wan and Yoda on Endor. Then Lucas decided hippie-haired, pervy-uncle-leering Hayden Christensen somehow made more sense. So that certainly paves the way for Obi-Wan's Force ghost to inexplicably appear as his younger, studlier Ewan McGregor self in current continuity.
None of this shit has to make sense...that's been established long ago (thanks, George). 
You can't discount anything at this point.
As for Mace Windu, I realize (as with Boba Fett) we never "saw the body"...but damn. That was a pretty high window he was thrown out of.
I suppose I could buy Samuel L. Jackson showing up as a Force ghost, as with McGregor/Obi-Wan above, a bit easier than I could the idea of him still being alive after Palpatine "unlimited power'ed" him out that window.
Mando could set Grogu on that Seeing Stone(?) and the "path" he chooses could very well be to stay with Mando? If Grogu abandons/walks away from the Jefi/Force life, that opens up some interesting things. Or, as with Ahsoka, Luke, Obi-Wan, Mace or whoever senses him might get some creepy vibes and all refuse to take the kid in, knowing he could easily be Anakin 2.0? Mando just might have a little sidekick longer than he planned. Get him a little suit of Beskar armor and have him be the Starsky to your Hutch, the Luke to your Bo, the Bear to your BJ.