Wouldn't you want a higher tax earlier to offset the higher EV cost?
A 1% tax isn't going to help if EVs are twice as expensive, whereas in 20 years time where hopefully EVs are approaching cost parity a 20% tax shouldn't be needed.
But on the other hand you want to broadcast to everyone that in the medium term your taxi will need to be electric, so plan accordingly. Taxes are hard!
Well you need to give time for market to readjust so the ramp-up is a grade period - but instead of doing it 1% per year you do it in 5% per year or some similar significant increment - this way you're clearly signaling what's going to happen without completely screwing people who invested in ICU.
A 1% tax isn't going to help if EVs are twice as expensive, whereas in 20 years time where hopefully EVs are approaching cost parity a 20% tax shouldn't be needed.
But on the other hand you want to broadcast to everyone that in the medium term your taxi will need to be electric, so plan accordingly. Taxes are hard!