Absolutely - for me it is a matter of "when" not "if" the FIAT value goes up....Bitcoin is going to continue repricing itself against FIAT values for as long as FIAT values exist...

I am currently working with an attorney on lease language that will more clearly address some of this model for protection for both parties of this type of agreement - though I really hope to have an "app" developed that automates this process and handles all the legal language through its use for each and every transaction... Yes I see this incentive structure being useful for virtually all transactions....

Anyway - back to answering your specific question a little more clearly....

When the tenant sends me say (using more round numbers for ease of math) 0.02 bitcoin valued in FIAT terms at $1000.00 and 6 months later that value is now $2000.00 the resident is able to recognize a 50% share of the $1000.00 of increased value....(right now I just reduce their rent due by $500.00 but with the "app" I have in mind they would simply be refunded or returned 0.005 btc which would be equal to $500.00

Eventually I think given the "return" or "refund" would be the easiest as it is in bitcoin but right now due to it possibly being a taxable event - I am hesitant to do it.... though this could be done in a federation (Fedi) or something similar which would make the tax thing a lot more questionable as to how it would be calculated which well...if this app had a large enough "mint" attached to it could eliminate the tax concerns from a user standpoint but from a government perspective well....that is TBD....I think it is likely governments come around and begin seeing bitcoin use much more favorably and remove some of the current tax issues....but that is my optimistic view :)