I can't see Lucasarts themselves making new adventure games (if only because Lucasarts doesn't really exist anymore since it was bought by Disney - the credits for Grim Fandango Remastered mention 'Lucasfilm' and 'Disney Interactive' instead of Lucasarts, but they didn't develop it of course - that was Double Fine (with financial backing by Sony).
That in itself isn't bad either - the talent behind those old adventure games left Lucasarts years and years ago. A lot of them went to Telltale (although I think all of them left - Mike Stemmle (Sam & Max Hit the Road) and Chuck Jordan (Curse of Monkey Island) continue to do some freelance work for them now and again but they aren't full-time employees anymore, and all the other oldies like Grossman have left Telltale at this point. The biggest concentration of old Lucas talent is still Double Fine, with obviously Tim Schafer, and a lot of the best people of that time like Peter Chan and Peter McConnell doing a lot of work for them.
They said in the past they would be open to do remasters of the Lucas adventures Tim didn't work on after they were done with all of the Schafer-games (Full Throttle will be the last one), but only if they could get the original creators involved. People from those days have always mentioned they'd love to visit Double Fine for a project like that, so as long as Day of the Tentacle and Full Throttle sell enough I'm sure we'll see more.
Ron Gilbert doing another Monkey Island seems unlikely to me, as he wants to own the complete rights to the series, and Disney just doesn't sell. Doesn't matter how small or obscure the franchise is, as a general rule Disney just doesn't part with franchises - especially not for the money someone like Gilbert could offer them.
To be fair, I always considered Monkey Island 1 and 2 to be great because of the writing by Dave Grossman and Tim Schafer (who wrote the vast majority of it) the art of Steve Purcell (who also did the Sam & Max comics - he works at Pixar now) and Peter Chan, and the music by Peter McConnell and Michael Land. Ron Gilbert is a great game designer and is a very big idea man, but to be perfectly honest I don't really like him as a writer. I didn't like the writing in the games were he was lead writer at all, like Deathspank. I mean, I think it'd be fun if Gilbert ever returned to Monkey Island, but to get me really excited I'd want Dave Grossman and Tim Schafer there. I think they were the real geniuses behind the magic of Monkey Island, and their later works really show that off.
Also, while I see Monkey 1 and especially 2 as easily the best games in the series, I still really like 3 (especially because Chuck Jordan, who was also lead writer for Sam & Max season 2 and 3, is just an amazingly funny writer) and, to a certain extent, Tales of Monkey Island.That last one suffered from a low budget and from being developed for WiiWare (and some narrative choices that are a bit 'eh'), but at certain points it hits that old magic, and it was just fun finally getting another game after the dissappointment that was Monkey 4 (which would have been a fine Sam & Max game - just a bad Monkey Island game. Funny, but a tonal mismatch).
