Heres an idea...

With regards to the timelock feature, you could have multiple options. It could be literally impossible to access your funds, or there could be other options where the funds are accessible (in case of emergency etc) but you place a self imposed and self determined percentage penalty if you take out the funds before the deadline, (the percentage penalty should be shrinkable as you get closer to the deadline as well in a proportionate manner). So you have established the option for a disincentivising system for the user to remove their coins early, and created a source of funds for somebody too! Where should the penalty go? Well the user should be able to choose this too. Either to the developers, or to be distributed to other users of the wallet. This would act as an interest acruing mechanism for everyone who deposits funds in the wallet! So everyones a winner and it incentivises more adoption as well.