Think of the development cost of such toilet paper holder.
Renault building just one for themselves vs also building more for other teams to sell or lease... Which do you think will actually cost more for Renault?
Mass producing anything can only bring down per unit cost. This is applicable to shuttles, stealth bombers or gold plated toilet paper holders.
The problem is that once you cease production, it’d be expensive proposition to try to buy more shuttles or B-2 bombers.
Just look at this from Honda’s point of view...
Would it be cheaper for them to develop a brand new power unit for indycar, or if they could just build more of their year old F1 engine?
I could be wrong, but I tend to think the later would be cheaper. Only issue would be legal... would F1 allow this? Probably not.
Anyway, just my wishful crazy thinking... I just think those 2 series need to work closer together one way or another. Sharing power units should make it cheaper for teams...