Given the gap between the development codes of the i3 and iX I suspect there was probably a lot of projects on the drawing board, however the fact remains that developing two bespoke carbon fibre bodies for single series production is not the decision of a bean counter.
Unless there's any specific evidence to the contrary, I'd say the Alpina was the only 'high performance' i8 as the information revealed about the Alpina i8 was basically the same as the rumoured higher performance one, and the rumours specifically around that version (or i8s) resolved to nothing more than the Formula E Safety car.
I suppose you can say it's the bean counters decision, but at some point someone has to check there'll be a sensible return on investment, and I'm prepared to trust Andreas Bovensiepen if he thought the amount of re-engineering required on the i8 was too high. Something that was still barely more powerful than a base M4 (and only some of the time), that would be costing quite a bit more than an R8, would probably have only attracted the similar criticisms as the standard i8 got.
I don't recall that, but if you're thinking of the i16, which was the production M NEXT based on the i8 chassis, that car was destined to get the B48 4 cylinder like the Alpina i8 had used... and it's that car that was "cancelled" before the XM publically became a thing. I know it got pitched as though they dropped one and did the other instead, but a variant on the X7 platform had been on the cards since it launched, Ian Robertson spoke about it at the time (low-volume, not a 7-seater). Early design sketches for what became the XM were from 2016 - about 4 years before the i16 was green-lit.
The way I see it, the production M NEXT (i16), and the X8 were both on track for production - initially just the X model, and the i16 after the reaction to the Vision M NEXT. Covid happened, profits cliff-jumped and panic ensued, the i16 was cancelled and they changed the direction of the X8, to try and cover both bases - hence it ended up being such an odd proposition for what it was. Essentially, we were always getting a big SUV, we just didn't get the i16 as well.