This is not how I saw the ending at all.
Technically, I was only going off of memory, because I found it an unsatisfactory conclusion to the show (though I liked it as an episode) and never went back to watch the final episode a second (...and third) time, so I was mostly remembering what was said about the finale, at the time.
But I've gone back to take a look, again, and--with both your interpretation and the manga weighing on my (per a quick look back in the thread) very sure-of-itself optimistic perspective--I'm pretty sure it's simultaneously both and neither: they definitely promise to stay connected and are both clearly in love with the other, and I think their mutual "I'll tell you when I've done what I need to do" moment is full of hope (that I would choose to interpret as "maybe that'll be our time," though certainly not a promise to wait for one another)...but the lines that close out the show ABSOLUTELY sound like "I"ll never forget you, person I'll never see again," which is the total opposite message.
A little have-your-cake-and-eat-it-too of them, in my opinion.
Regardless, the manga is very clear that their relationship--friends or otherwise--is DONE. Akira goes back to track, which means she's no longer at the restaurant, and, unless we read into her using the parasol (which, given the context of that final panel, we'd have to really
want to do), no longer keeping Kondo in her mind as anything but a memory.
In slightly other news, it
does earn her going back to track, though, which I never felt the show did. It's also very clear about the severity of her injury--and how likely it would be to come back from it. So, her reluctance is half fear of not being able to get back to 100% (which sucks if you're as naturally gifted as she is) and half being in love with Kondo, the latter of which she often uses as an excuse not to admit the former. The show keeps her injury's details so hidden that it actually muddies the justification for how "go back to track!" is the solution and makes it rely more on an audience assumption that she "obviously
has to go back to track" because it's more comfortable to assume her affections for this much older man are deflection instead of genuine. (Which I never liked. Because it's boring. And undercuts Kondo's character.)
But I'm just rambling, at this point.