StreetComplete tags source:maxspeed (in UK)

My app StreetComplete currently tags roads that have no explicit speed limit with source:maxspeed instead of maxspeed:type in the UK.
This has been identified as a problem in issue ticket #492.

To summarize the linked ticket, I now - instead of creating a special exception for UK - lean towards using maxspeed:type for the whole world. (see my rationale here)

There is one open question though and the original poster did not answer anymore, so I am asking here:

Can maxspeed:type=nsl_single and maxspeed:type=nsl_dual always be inferred from oneway=yes/no (+highway=…)?

If not, what can the user of the app be asked that results in that tagging respectively? (The question must be answerable by anyone, so also non-UK-citizens and children)

And, finally, if it turns out to be “too complicated / not easily answerable”, the question is, would you find it okay if the app simply tags GB:national (or even GB:urban/GB:rural) and leaves the detail to more experienced mappers?

P.S: I am posting a link to this topic in the German forum (because source:maxspeed originates from Germany), I feel I shouldn’t leave them out when I make such a change in the app.