Clearly one argument against expanding beyond ASCII would be disagreement over which letters to include! My preference would be where possible to stick to non‐precombined characters; thus we'd both be ok with ⟨Þ⟩ or ⟨Æ⟩, but I'd avoid ⟨Š⟩ and ⟨Ä⟩ whereas you'd (presumably) take exception to ⟨Ƿ⟩ or ⟨Ꞵ⟩ (assuming those even show up for you).
One valid use for beyond‐ASCII letters imo would be expanding Betza beyond the square board; we have few enough capitals left that e.g. ⟨Ⅎ⟩ for ‘ⅎiceroy’ or ⟨ẞ⟩ for ‘ßexton’ (both of course Gilmanese) might be in order. And since the ID doesn't do non‐square boards (except through hacks as for Chess66) it wouldn't even need to worry about them. Likewise the non‐square directional qualifiers (I'm maybe grasping at straws a little with ⟨ɂ⟩ and ⟨ƿ⟩ for ‘up’ and ‘doǷn’, but non‐ASCII letters cover an odd sound space…)
There is no such thing as a 'regular keyboard'
Especially when you have people like me who (heavily) customise their layouts; all the characters I've just typed (except the quotation) are accessible for me without copy–pasting
Clearly one argument against expanding beyond ASCII would be disagreement over which letters to include! My preference would be where possible to stick to non‐precombined characters; thus we'd both be ok with ⟨
Þ⟩ or ⟨Æ⟩, but I'd avoid ⟨Š⟩ and ⟨Ä⟩ whereas you'd (presumably) take exception to ⟨Ƿ⟩ or ⟨Ꞵ⟩ (assuming those even show up for you).One valid use for beyond‐ASCII letters imo would be expanding Betza beyond the square board; we have few enough capitals left that e.g. ⟨
Ⅎ⟩ for ‘ⅎiceroy’ or ⟨ẞ⟩ for ‘ßexton’ (both of course Gilmanese) might be in order. And since the ID doesn't do non‐square boards (except through hacks as for Chess66) it wouldn't even need to worry about them. Likewise the non‐square directional qualifiers (I'm maybe grasping at straws a little with ⟨ɂ⟩ and ⟨ƿ⟩ for ‘up’ and ‘doǷn’, but non‐ASCII letters cover an odd sound space…)Especially when you have people like me who (heavily) customise their layouts; all the characters I've just typed (except the quotation) are accessible for me without copy–pasting