It's too late, the window for custom games to be re-launched into the "mainstream" was if Reforged did well to not only in sales, but in energy and Blizzard and community members worked together in that way. They would have to hit a home run internationally in reviving/energizing the community, not just in sales but also in public image through Twitch/YT/social media as Dota 1 and other custom games were still holding on. At this point, the infrastructure of the Dota 1 community and other competitive custom games have mostly moved on to being niche.
During my role in being one of the bridges in community feedback and devs, I actually had plans of assembling teams for this (custom game & blizzard cooperation, with DotA 1 being the first target). I made some progress on the community side assembling a team with the needed DotA leaders to make it possible, but personal things happened and I became inactive. But I'm obviously not even a part of the bigger puzzle: resources ended up becoming spread too thin anyway for the team's attention to support esports & more for specific custom games, amidst all the Blizzard issues (cutting back funding, talent turnover, controversies) and the Reforged release state killing the chance.
It was a long shot but it DEFINITELY was not impossible, there were pieces in place! But right now, there is no profit in it, and the PR goodwill of it will be minimal this late. Microsoft's turn though right? </3