And if you implement this you can keep the 2d20 mechanic specifically to represent skill training.I spoke about it in another thread, but the way Shadow of the demon lord handles Dis/Advantage is really the best of both world. You gain Advantage or Disadvantage dice depending on the situation. They are d6s and they cancel each other. When making a roll, you also roll the given number of d6 and keep the highest roll. You add/remove (depending if its an advantage or disadvantage) to the total you rolled on your ability/attack roll.
Yeah, I wish my players would accept to give a look to other systems, especially games that are not that different from D&D. We played Fantasy AGE and Beyond the Wall a little, but since we started 5e, they seem less interested in other systems. So my SotDL is there on my shelf, gathering dust.And if you implement this you can keep the 2d20 mechanic specifically to represent skill training.
Although unfortunately if you used this system in 5E you'd be missing out on one of the best aspects of it in Shadow of the Demon Lord - the way it's implemented throughout the whole system.
I don't know if this is out of the scope of your project, but I would love to see revised XP and encounter building rules for DMs, character wealth suggestions, and magic item prices.
A better investigative and social suite of skills.
And a better depiction of armor.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.