Some thoughts after using it extensively for a few weeks now and in multiple different scenarios:
While I like the changes to collections and gamelists, I am not convinced this is the necessary step to take. Right now I would say the number one issue that's holding the launcher back from being open the a mass audience is adding games. Currently, my flow to add a game is add the rom file to my folder, scrape the entire folder again (which takes sometimes as long as 45 minutes on large collections - it has to scrape everything each time due to Pegasus using it's own media file structure), run a script I had to write to organize the media, take the gamelist file the scraper made and drop it in the conversion tool, then replace the metadata.txt with this new info (and if I've made any changes to specific games those will get overwritten unless I'm very careful). This is just to add one game.
The only reason willing to do all that work is because I really see the potential in the launcher and think it will be the best launcher hands down when all said and done.
So combining the collection and metadata sounds good when looking at it in a bubble, but if anything it will make it more difficult with the current workflow. The same goes for multi-disc games - fantastic addition but unless the workflow is made more streamlined it will potentially get in the way more than it currently does (if it were to read .m3u files that might be more convenient).
I guess what I'm getting at is if you have a roadmap for features, working on how users add games should be a top priority. If these changes are necessary in order to reach that goal then great, but ultimately having users manually edit text files should be an absolute last resort for any usable piece of software in my opinion.