Does every target you have interdicted escape in this way? I think not. If they escaped once they can keep escaping, a fact which you know for certain having played the game for as long as you have. Personally, I would just have considered them "not worth the effort" and gone to find another target as a small yellow guy with pointy ears once said, "Time is money, friend."
How about this: if you want to allocate an internal slot for an FSD scrambler then I can allocate an internal slot (likely a cargo rack) for an FSD shield that prevents it being scrambled. Then it's a straight up arms race as large elements of the game already are. Sound fair?
They can, but they might not. Every attempt is different. Coming out of warp, I may be right on top of him. We might be facing each other, we might be facing away and 2km from each other. The distance and direction is different. So no, just because he got away once does not mean he'll get away again. And if I can do a little damage each time (or just drop shields and launch limpets), that 4th interdiction make make him open to negotiation with only 30% hull left. But, it depends on the circumstances. And don't blame me for their poor planning. Rather than warp to another system, change course, drop out of warp quickly then change to another system, they simply keep on keepin on. They think they can hold the course and not be interdicted again. That's their own foolish fault.
A submit, boost, warp player won't ever succumb to any piracy attempt, ever. Not because of their tools, but because of this 5 to 8 second mechanic. To simply say "ignore them and pick another target" is ignoring the issue as a whole.
And yes, your idea sounds absolutely fair and I have no problem with it. Fact is, just like now with shields, money hungry traders will forgo the FSD anti scrambler and they will make for easier targets. The tried and true traders will have these equipped and they will be tougher to interdict... but with good reason because of an equipped module, not some weird mechnaic. At that point, I can't say diddly as the TRADER was properly equipped. If I ask for a second warp scramber because it's so hard, then you know I'm just a whiny troll.
So no, I have no problem with your proposed idea and think it would make an excellent addition to my idea of a proposed FSD scrambler. You need the balance otherwise it's an I WIN button.
It does seem that an ASP is what I need to be using for pirating. Perhaps when I get one of those, this "problem" will go away. But it will still remain for cobras cmdrs who engage in piracy or even bounty hunting.