I don't think this works.
It is a quickie "Oh, shove something in there, Fred, we need something that'll do" fix.
The problem is, saying that all 1957-1966 stock is Era 5 will just confuse people. Hornby give the catalogue numbers of suitable stock to run with locos- so that you run SR Coaches with SR Locos, NSE 50s with NSE Mk. 2s etc.
If I don't have a clue about railways, I won't know which models are passenger locos, and which are freight, and, for BR, which region suits an engine- I could end up with a "Lord Nelson" hauling maroon Thompson coaches (O.K., it probably did happen, but not a lot). I could have a 1920s SR N Class in Olive green from "Era 3" hauling post-war GWR coaches, also from "Era 3". Lumping things into "Eras" is no use.
Take, for example, Continental railways. Now, I know next to nothing about Continental railways- if I could afford anything, it would be bought on a "Ooooh, that looks nice basis" because the catalogue is devoid of information. Saying an NS engine is Era V doesn't assist me. Is it passenger? Is it freight? Is it container freight? Petroleum? Vans? Prototypical running of Continental stock going by the catalogues is hard unless you have plenty of books, and/or can afford to visit your chosen area- by which time, you;ve probably become a railway buff about whatever it is you like, and you therefore do not need the Era system.
Nice try, but the wrong way to go about it- they should copy Hornby's method.