The quality of the base is a fundamental aspect of the manufacturing of a quality silver halide product. If the base is not perfect, you cannot coat a flawless paper on it.
It affects the evenness of coating (homogenity), coatability in general (coating tear offs, stripes, bands, adhesion), surface gloss, evenness of gloss, DMAX and of course the whites (light tones, color).
These are only the physical properties. For the chemical properties, we have the demand of no interactions with the silver halides, or the paper goes into fog over time.
So it is not a question of whether we can coat onto a different substrate (yes we can), but rather which image quality can the paper (still) deliver if coated onto an alternative substrate.
Forte ceased the 300g version in 2002 (!). We sold more paper on 250g after this date than we ever sold on the 300g base. The 17% less in weight is difficult to even feel.
I am afraid we are talking about a rather limited market potential here which will most likely not offset the implementation costs in producing the base.