When I heard you wanted to do your own proposal I thought "thats lame he must be mad about something" but honestly what you are proposing its exactly what I said day 1 of the release of Soulbound reward cards.
Its the only way to really deal with bot farms and at the same time reward top players.
This is probable the best idea about SB reward cards out there currently.
I fully support it.

Theres a harder version of idea this that reads "you could only unsoulbound a card if it is maxed" but that will piss a lot of people off.