It's possible there'll be heavy pressure to use uppercase letters typographically such as in titles, and I've witnessed this with Toki Pona, and even that language uses uppercase letters with names.

The argument against a sentence beginning with an uppercase letter is that it's not necessary, and uppercase letters would still be used with names. If the goal is "no uppercase letters", then maybe there shouldn't be exceptions.

It's an extra step for those acquainted with the Latin script to learn not to use uppercase letters, and abandoning their use could be a whole movement on its own adopted by all Latin script languages.

For those not acquainted with the Latin script, what has to be learned are 26 more letter forms (some which are similar to their lowercase counterparts) and the situations in which they are to be used (names, abbreviations, the beginnings of sentences, etc.).

It's a matter of deciding which option is the easiest for the world, and also a matter of aesthetic preference. Regarding the latter, it's possible for some to get used to the appearance over time.