Let's face it. From a creators perspective, having Tenchi choose someone is going to piss people off. If he chooses Ryoko, you loose all these other fans. If he choses Aeka, the same. It isn't a winning scenario.
That said, it is pretty clear that Kajishima-sensei's choice was to have everyone be with Tenchi because that's what he likes. Look at all his other anime titles. Everyone of them has a harem ending save maybe Masquerade, which actually has a 2-girl ending with the possibility of more in the future. However, being an H-title, the lead there did sleep with all the girls so...^_^;;;;
I think that in K-sensei's H Tenchi doujinshi, the reason he had Tenchi with Noike was to thumb his nose while giving the bird to fans to (1) don't like Noike and (2) want a specific choice and not a harem solution.
There are titles were a guy makes a choice. Some, like Ai Yori Aoshi, the choice is made from the start, but the situation has to play itself out so that a harem grows and then dissolves.
From a story perspective, I've already laid out why the harem end is the one that works best for the story. I don't think we'll see any more "OVA" episodes starring Tenchi and company though. Assuming Saint Knights Tale ever goes into full production, we'll likely see Tenchi again, but I can't imagine Kajishima-sensei going back to the Tenchi well for a pure Tenchi title. I can see him maybe doing a 4th novel (not counting the GXP novels) about Mihoshi but even that's a very long shot.