I understand why it doesn't exist because it's pretty niche and a shitload of work, but I wish there was a a really good dedicated 2D animation software similar to Moho Pro or Toon Boom Harmony on Linux. That's one of the only reasons I'm still keeping Windows around.
Also as a side note, don't trust Toon Boom. I bought a perpetual license from them that was super expensive, and then they switched to a subscription model and turned off my perpetual license.