In Reformed Esperanto, and also at the start of Esperanto, Zamenhof wanted to introduce plurals using -i instead of the Greek influenced -oj. Was he planning on introducing another infinitive (like Ido does with -ar) and scrap the current Latin -i, or just introduce ambiguity into the language?
According to the page 19 of Pri Reformoj en Esperanto:
[...] Mi proponas: per la infinitivo -a (i estas okupita por substantivoj; r, kiu estus pli internacia, prezentus malbonsonaĵon); [...]
Which translates roughly to:
[...] I propose: with the infinitive -a (i is occupied by substantives; r, which is more international, presents as awful sounding); [...]
Because Zamenhof made adjectives and adverbs all end in -e (making their meaning depend on position) in Reformed Esperanto, he was then able to use that free space to infinitives, which kind of makes sense if you think about the present conjugation -as.