The spaces problem can usually be worked around easily, the dll solution still exist, unsure why you say otherwise
As far as the suggestion is concerned, it's not about the difficulty of the implemtation, it's about being consistent, in the past, all commands could be called as identifiers, this functionnality was removed because it would allow users to easily get owned, by $quit for example. So bringing back the feature which was removed for 'security' reason would be a bit illogical.
It can be argued that only the commands mentioned in the suggestion could be made as identifier, but I imagine you would quickly start seeing people suggesting others commands, and it wouldn't really make sense to accept one and not the others.
Also keep in mind that if mIRC wasn't handling spaces the way it does, it would be a much bigger pain, you would have to use $trim everywhere and handle the removal of consecutives spaces yourself, you DO want mIRC to handle spaces the way it does 99% of the time, it's better that way.