I like the philosophy of having a universal auxiliary language, though I doubt it will ever get to that point.

At the present moment, I believe that the closest human beings will get to a universal auxiliary language, is probably something like Interlingua. It's probably easier to get people who are interested in languages, to learn a language which was specifically created to help them to communicate with speakers of multiple languages at once (such as Interlingua for Romance languages like Spanish, Italian, and Portuguese), rather than try to do the opposite by trying to convince the whole world to learn a new language. With a language like Interlingua, you won't be wasting your time even if you can't find other speakers, since it'll help you understand other Romance languages more.

As for Toki Pona, I'm not sure how long the simplicity will last if the Toki Pona community keeps adding more and more words.

According to The Online Etymology Dictionary:

Old English dyde, past tense of do (v.). The only remainder in Germanic of the old linguistic pattern of forming a past tense by reduplication of the stem of the present tense. Far back in Germanic the equivalent of did was used as a suffix to make the past tenses of other verbs, hence the English -ed suffix (Old English -de).

It's interesting that a similar thing didn't happen for the word shall or will, in order to create a future tense. For example, using a suffixe from "will", like "-ll" or "-ill" for a future tense.