I think there needs to be a bit more of Saudi Arabia, if you want to include the Nabateans.
Other than that, it should be fine for Rome from its foundation all the way to the Empire's height.
Napoleon basically did that in order to help sell the metric system to the French people.
https://en.wikipedia.org/wiki/Mesures_usuelles
The US has partially decimalised the imperial system into the US customary system of units.
Similarly, China also decimalised its measurement system...
Short of there being a devolved Ulster within Ireland, which has the ability to nullify literally everything Dublin passes from applying within Ulster, without any possibility of Dublin being able to veto it, anyway.
Which I doubt even the most pro-compromise Home Rule-er would agree to.
From what I understood, they were willing to give Ulster a disproportionately large number of seats in the Dublin parliament as a compromise. Obviously, even that wasn't enough for the hard core Ulster Unionists.
Then there's the issue of racist racists being all racist and stuff. The North would probably argue something like "well, if you aren't going to give them political equality..."
IDK how true this is, but IIRC, one of the reasons why Welsh did so well, when Irish or Scots Gaelic didn't, was that it was used a lot more commonly in churches and in Sunday Schools.
I suppose the fact that there wasn't such a massive outflow of Welsh speakers compared to Irish or Scots...
Thing is, the Glagolitic, Cyrillic and Gothic scripts were invented (at least in part) with the goal of converting the Slavs, the Slavs and the Goths respectively to Christianity.
Still, there's no reason why there couldn't be alternate Greek-derived scripts adapted for the use of the Slavic...