"Fix" issue of people not voting by reserving 4/15 filing date for those that vote, if you can't or won't then due 3/15.
The tax code an easily be tweaked to encourage people to vote without affecting tax rates or revenue received.
Here is an easy example:
Currently 4/15 is the tax filing date for all Americans.
Let us reserve that date for those that participate in American governance.
If you vote in that years Primary (May) and Election (Nov)
then you participate in American governance and your taxes may be filed by April 15th.
If you only vote in one of the two possible elections then its April 1st.
For all others regardless of reasons or circumstances March 15th.
The total tax due is not changing just the due dates.
The above proposal can be tweaked to accommodate politics