I don't see anything wrong with imposing a minimum amount of coins kept in the wallet 100% of the time. People can buy more coins to trade with. Seems fair considering the bagholder payouts are decent.
This should end the cycle of pump and crash near the times of payouts while creating a healthier trading scenario.
If you are talking about a percentage of total coins need to be kept, such as if I have 1000 coins, I need to keep 25% of that in my wallet all the time, that is certainly one alternative. That is doable, although that could add to a bit of confusion when it comes to payout time (such as someone buying a ton of coins before payout, then wondering why they aren't getting rewards that month).
If you mean keeping the entirety of your coins in the wallet 100% of the time, for any reward, I'd be against it. For an extra bonus, sure, it's fine ... just shouldn't be a requirement for payout though.
There are other things they could do too, if they have the funds available. Such as contests -- perhaps those who keep the majority of their coins in their wallet for the entire month could be entered in a raffle for nice items, or something like that. That would fall under the 'bonus' idea I mentioned, where it's sort of a nice extra, but not a definite requirement.
I was thinking if you need to have 1000 coins for bagholder status, this should be the minimum balance per month to receive bagholder payouts. I thought this was the original purpose of the coin. Think of it like a term deposit in a bank. If you don't touch the funds you receive the interest payment for whatever interest rate/time frame you have chosen.
Should people be rewarded for keeping a higher amount of coins permanently? Absolutely. Not sure about the logistics of such.
Those who want to day trade can buy more coins.
You don't want to stabilize to the point of flat lining the price but you still want to encourage trading, especially buying.
If people know they can receive a (somewhat) guaranteed income from their savings, more people will invest. Bagholding may not be the best terminology either.