I like the way you think... because you almost read my mind.
I have developed a game after trialing various options along the lines of multiple rail requirements and bonuses for a couple of years.
The problem with points per rail with more than 5 balls on the table is that there are a lot of collisions and it looks a bit like a bashfest.
In the game that I feel achieves a great balance, at this stage, is based on straight pool, each rack is a race to get the highest score.
The first 10 balls can only score 1 point. To continue on a break, a player must, in addition to pocketing a nominated ball, either move another nominated ball or hit a minimum 2 rails (with CB or OBs).
On the last 5 balls, the same rules apply, but if you nominate 3 rails and hit them, you score 2, nominate 4 rails and hit them, you score 3 and so on.
So a player may make the first 11 balls, but the incoming player can still beat them with 4 x 4 rail shots or any other combination that obtains the required points.
This is not easy, probably a 35% chance for a pro, but it would result in some pretty exciting and spectacular finishes to frames. Getting to a 12 ball run (with a likely score of between 12 and 14) on the break would be a bit like making a 73 in snooker, whereby one can only get beaten by a quite miraculous 3 ball finish of say 4,5 and 5 rails in addition to the pots.
To get the big rail scores, like 5+ usually a bank off 1,2,3 or more rails is required. Here is a 10 rail shot I did recently, which is maybe a 15% shot if one manages to get into the right position for it and is familiar with the angle required to make the 5 rail bank.
https://www.youtube.com/watch?v=n_BhOk_IFY0
Getting something like this in a game would be quite rare... something akin to a 9 dart leg or 140 snooker break, but worth a try if you need 9 points to win the game.