I wish Stellaris would have more accurate population numbers and not abstracted. It also is weird how some planets just stop growing after a while. Would be great if there would be no hard caps, only soft ones.
It could actually be done without scrapping current system. Just keep current system and add in-depth view which would have more information. So if planet has 30 population, in in-depth view it could have 30 000 000 or 6 342 415 257 citizens, or more if it keeps growing. But you could only manage the 30 population which are abstract representation of 30 000 000 or 6 342 415 257 people etc. And depending on species, 1 population could either be 1 000 in detailed view or 100 000.
It would just be immersion thing, at least initially, but could be expanded to more detailed system. And immersion is important.