Automatic spacing correction for locl FRA. Good or bad?

I am designing a font family and thinking about adding a OT feature for French only, allowing to substitute in few specific cases the normal space with a thin one, as in French should be.
I’m planning to do it with a ligature-like substitution (sub space guillemetright by space_guillemetright.loclFRA;) inside locl{} language FRA. I could even do it with a contextual kerning, whatever…
It would be particularly useful on the web or software other than Indesign, where it’s a pain to type « thin space ».
My question is not about the technique but if it’s a good idea or not.
I’m discussing with some graphic designers and type designers I know but can’t find a solution. Some of them tell me “NO: you have to leave the work to the typographer”.
However, in real life I see that people don’t know how to type thin spaces or even don’t know they have to + on the web it’s a pain even if you know the rules.
Even for me knowing the rules, it’s a pain to type “thin space” and I’ll appreciate it comes straight with the font.
What do you think about it?

In Germany, we use the guillemets without spaces so I sometimes kern them apart a bit. Why not kern them closer there is a space? You only need to make sure that you ‘fix’ is not applied in the wrong context (like in German where they are used the on the opposite side and the space would be to the next word and not to the one where they belong) but using a language FRA should fix that.

sure I was thinking of limiting it to language FRA.
So you suggest a negative kerning between space and guillemets? And it should work as webfont too right?

but, wait a minute! Are you suggesting to use the kern OT feature? And how to manage my 5 masters that need different kerning each? :confused: