Doesn’t the factor sleeve already do so? Looking at MSCI indexes Value, Momentum, and Small Cap are underweight USA. Quality is still overweight. For example, the MSCI ACWI Enhanced Value index only includes 20% US stocks.
Of course there are factor products that fix (or at least tether) country weights to those of a market cap weighted index. Notably AVWS.
Regardless, it makes some sense for now to split into US and ex-US (Dev-ex-US and EM) to get Swiss tax credit for the withholding taxes paid to the US. A problem that might get solved in the next few years (check: Reclaim withholding tax on Irish based ETF?).