system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] If the Doctor's TARDIS is an antique, what are newer, more contemporary TARDISes like? (Speculation allowed)

We hear a lot from other Time Lords that despite being "the most powerful ship in the universe", the TARDIS is an antique, a heap of junk, and from her own perspective, a museum piece when the Doctor was young.

When we see other TARDISes, though, they don't seem any different, other than some visual differences. So what's different about the newer ones?

Speculation/Headcanon allowed, since I don't think the show goes into much about it at all.
gpt
One perhaps underappreciated feature of the Doctor's TARDIS: Able to keep (mostly) working for hundreds of years without going to the shop. No maintenance beyond what the Doctor can do him/herself. 

I wonder how long the advanced features on late model TARDISes keep working when they're cut off from the civilization that built them?