Rumor has it the new Gremlins 3 script is a reboot. Here are some quick notes for a treatment of Gremlins 3 as if it were a proper sequel:
Gremlins 3 could start with footage of the first lunar landing and show the supposed missing 2 minutes of footage which features long shots of a Gremlin or two in background. CUT TO: PRESENT DAY-Dark Side of the Moon. We see the active thousand year old Gremlin Lunar Colony.
The Gremlins fly down in a 're-commissioned' MTV satellite to steal the Presidential 'Football' and Gizmo hitches a ride on their craft as they head back to the Moon. (Gizmo was getting the medal of honor at the White House for acts of bravery) They are able to rewire it so we can't disable it from Earth. (scene would occur directly after the opening showing of the 'missing 2 minutes' of NASA footage.)This would further bolster the origin mythos surrounding the original film-Little green men from space. Billy & Cate go to the moon via SpaceX (with a team of course) to retrieve the Presidential Football and Gizmo, now held prisoner by the Gremlins. (their quick trip to the Moon scene would pay homage to 'Nothing Lasts Forever' via Billy Murray cameo)
The Gremlins routinely apply water to one Mega-Mogwai in order to make more of them so they have plenty of food. That one Mega-Mogwai, known by the Gremlins as 'Soupy' befriends Gizmo. Gizmo feeds Soupy after midnight somehow.... And the Mega-Mogwai in both regular form and their new Gremlin form fight the Gremlins for their freedom while Billy & Cate & Gizmo try to retrieve the Presidential 'Football'.
Feel free to add your own ideas to the concept notes!