Darek
Very good idea. I'm trying to incorporate a similar one in my league, and only with the last two laps without KERS, but the players put up a lot of resistance.
If they aren't supportive, you'll struggle. You need the support of all the members. Initially I tried it for 1 season but there were a couple of members who didn't like it and kicked up a fuss about it so halfway through the season I gave up.
I had second thoughts though and applied it to the league rules for the following season. This time, there were no objections and I had the support of all the members.
It works really well but you need that support and I'm not sure that banning the boost in the last 2 laps will work, it needs to be longer for it to have the desired affect. If someone is closing in at 0.2 seconds per lap but they're a second behind, 2 laps isn't enough to make a difference. You need that 15% in order to make the closing stages exciting