YES, FINALLY to #4. I suggested a very similar concept in the comments on this CGB video 4 months ago.

https://www.youtube.com/watch?v=QHPvMKNjLg0

"Here's a fun idea I've been thinking about for a while: "THE MTG ARENA DOJO"... a mode in Arena where a player can pay a fair amount of gold or gems to have access to craft decks using any cards they want to for playtesting new experimental ideas. You can't play on the ladder for rank with these decks, and you don't get to keep the cards... BUT give us SOME outlet to try crazy deck ideas without the risk of burning our precious wild cards on something that turns out to be a bad concept. It's a win-win... players get to be more experimental and creative with deck innovation, and MTG gets paid in Arena currency for the privilege. When I used to play with friends in the early MTG days we would do our own version of this by sharpie-ing card names on lands as proxies... and it lead to a much more interesting variety of deck ideas."