I'm not so sure that it would be prudent to produce Scottish Lowland troops of the sort that Margaret (probably) had in her army as they wouldn't look so different from the English troops as you know Arlequin.
The devil is in the detail, Northern English and Scots troops would obviously look slightly more rugged and less effete than their Southern counterparts.

Joking apart, I think it's largely a case of 'poorer' looking rank and file, which could be covered by a 'Levy' set. The current WotR Infantry do cover a wide range of 'social classes' as it is, but the bulk of them strike me as being quite up to date in fashion terms for the time. I could be wrong but I imagine that the more rural parts of England, the North and the Scots Lowlands 'might' look a bit dated and scruffy.
How far you could go down this route by mixing and matching with a HYW Infantry set remains to be seen. The Perrys are of course very much into all things Medieval, so if there is anything approaching a glaring omission, they are already aware of it, so anything I might say is actually redundant really.
I'm pretty sure you're right with the other minorities, Mortimer's Cross and Stoke Field both saw large numbers of 'Irish troops', of which a reasonable number might have been 'English' from the Pale and I can't see enough call for the 'native types' to warrant the expense of producing a plastic set.
I have no doubt that further plastics for the HYW period will be forthcoming and what would a French Army be without massed ranks of French Men at Arms? I would imagine that the range will probably expand to around the same size as the WotR one myself.

The 10% ratio is fine for bigger battles, but you'd expect that to shift significantly to the right if you're doing a skirmish game based on a confrontation between magnates' military households.
Most definitely! I doubt that the 'professionals' and 'semi-professionals' within a noble's household and those of his retainers, would be that vastly different in composition to comparable and more formally organised continental 'lances'.
So a 'Knight', a slightly less well-equipped 'second' (who in many cases appear to have been an archer rather than a 'lesser-man at arms') and between 1-3 archers, all mounted - at least for travel purposes, is probably the ratio we are talking about as the core of any WotR force.
Once you start adding in recruited or indentured companies of infantry then the ratio shifts. However the general ratio of 'Men at Arms' to 'others' across NW Europe at this time ranges between 1:7-1:10, so the English were hardly unique in this respect.
Nevertheless as you say, depending on situation and circumstance, 'every' engagement did not involve the full range of troop types in their overall ratios, whether in the WotR or Continental wars.
... Captain Blood still needs more archers though.
