My main issue is this is quite complicated.
People with soulbound still have to pay for the actual land and the actual DEC they stake on it. If they have 100 accounts with 43/86 soulbound cards on they have to buy 200/400 land plots to actually use them, which is already a huge investment, ignoring the DEC. They also probably wont have max level soulbound so they pay again from the inefficient cards (although in time they will of course max them)
Why not just make staking requirement higher just for soulbound if it really would be such an issue? I think this is easier to understand and doesn't introduce a new system.
RE: SPS Governance Proposal - Require DEC Burn for Soulbound Cards to be Used on Land