Microsoft tried it already with 8. REALLY really tried it with 8, removing 7 from everywhere it only could.
It was a disaster. PC sales crashed. As we discovered, forcing 8 on people did result in marginal increase of sales of 8, and a massive reduction of sales in PCs.
Finally someone important at microsoft realised that in winning the battle of 8's adoption over 7, they were losing the war of keeping PCs being the primary customer computing platform, and 7 was quickly pushed back into OEM chain. I think that this particular lesson was painful enough for microsoft not to even think of trying it again for at least a few years.