I think that could likely be helpful for some people, but probably not in my case. I don't expect anyone else to be working alongside me.

But I imagine a solo founder wanting to start on a low-cost individual plan, and expects to eventually add new members when he/she gets a co-founder and/or more team members.

In any case, people like the feeling of there being an easy "on-ramp" to what they imagine they'll do in the future. GitHub in particular has achieved mastery of easy on-ramps to more (paid) features.

I'd be curious to find out how many Trello boards start out with 1 person and others join weeks or months later.