re cable shifting and crud tolerance;
except for 4700 series, shimano 2x10 uses the same RD shift ratio as 6,7,8,9s systems. When you are pulling just 2 point something mm of cable per click, it ain't much. Between that and underbartape cables it is an inherently finicky system. 2x11 uses a different shift ratio and is far less demanding in terms of cable condition.
With the correct shift ratio, I don't see any reason why a 12s (or higher) system can't be shifted via cable.
The other side to the coin is the inherent nature of the chain and sprockets. It doesn't matter how the shifting is done if the chain and sprockets don't tolerate average road conditions.
Not everyone knows this but as well as using different shift ratios etc shimano MTB systems often use a slightly different sprocket pitch and slightly different chains etc. The reason is that they are required to have more mud clearance. You get that mud clearance and more 'for free' if you use (say) an 11s chain in a 10s cassette.
If you are commuting or training and don't need all those gears (and/or can't be arsed to clean them) then it makes sense to use fewer sprockets. 8s yes, but if you use a 6s system it probably won't need fiddling with from one year to the next.
I need hardly point out that a 2x6 system can offer the same ratios as a 1 x12, do I....?
cheers