Mitas were doing a 150/70-17 in the E07 and I think in the E09 as well. The new E10 comes already in a 150/70-17.
The 140/80-17 sizes are cross ply I believe, and the new E10 is a bias ply, a combination of cross ply and radial ply. The 150 versions of the E09 and E07 will be Bias ply.
The downside for us is that Bias ply produces a stiffer carcass, so they make the rubber compound softer to get the ride and handling on road.
Hence the initial issues with the E10. Mitas has apparently changed the compound from the super soft one used in the early E10, that caused so much poor feedback from users.
Using a 140/80 in place of a 150/70 produces no real issues. The tyre tread face is spread flatter. I thought this would be an issue on road, but I can scrape the pegs without running out of rubber, and the flatter contact area seems to make them last longer on the wide rims than they do on narrower rims on lighter bikes.
Speed rating wise it isn't a problem here as we have a 110kph maximum. It sucks. The previous unlimited speed limit in the Northern Territory was replaced with a 130kph limit, but I hear they are going back to a unlimited limit outside of the main cities (towns). Previously you couldn't legally fit some tyres here if they didn't meet the manufacturers speed ratings, but with the NT capping their limit at 130 it helped open up tyre choices.
But it was only ever a problem if getting a reputable dealer to fit them for you. Fit them yourself and you fit whatever you want.