'he said now it [15x18] doesn't need to be addressed'
that's not what jackles said. that's like, a smallllll snippet of the entire thing. he essentially, in my opinion, said the Testament aka cas' Declaration and proof of love [i find it interesting he corrects himself from confession to testament by the way when we all call it the confession, he calls it a testament, which is astoundingly amazing] stands as it is, and that their love for each other is going to basically be understood when they're reunited. They don't need to have a sit-down chat or long-winded therapy discussion about their feelings.
We, the audience, also know where they both stand with each other. This concept that they'll get Cas back and he won't know that Dean loves him back is astounding to me. Jackles is saying essentially that they're each other's people, that they found each other, that they keep finding each other, and that when they reunite, both of their feelings will be understood.
And that dean understands. When they reunite, it will be understood that dean understands. He didn't say there wasn't going to be reciprocation, just that Cas' words don't need resolving.
Aka, what's changed from previous answers he's given? From "let's talk about that goodbye" to now? I'm being mostly serious when i say, i think they've outlined that scene or have a rough outline on how that scene is going to go and he's trying to give an answer without giving away the store lol.
I say this because this was a pretty detailed answer, in my opinion, and him calling Cas' words a testament instead of 'the confession' also makes me think there have been some conversations.
i know that assumption is wildly speculative because who knows where they are in the continuation process behind these scenes but given the fact that it's actually quite useless to even have a continuation unless they follow up the destiel arc and finish up that storyline, i do think it's been top of mind for everyone involved. Yes, including jackles. Don't even get me started on him correcting that fan who shouted subtext with text.
he was being thoughtful in his answer and trying to find the right words, in my opinion.
The half-jokey way I'm going to end this is: Dean is gonna run up to him and give him a big ol' hug n' smooch.
Joking... but also not joking at all haha.
But Dean's also a man of action and his love can be seen through those actions and if a man is going to hope universes and try to potentially jailbreak into The Empty to get me (if that's what they wind up doing which I thnk they are) that's love in my opinion as well. He's done that also twice in Purgaytory, ignoring an easy way out until he found Cas, putting his own well-being at risk, and also ignored a time limit and risked getting trapped in there because he couldn't find Cas so...
Suffice it to say, I also think in general, you just gotta give the man some faith and just see what happens.*
(*but also, it'll never be 100% how we wrote fics or speculated in our head, nor should it be; storytelling is an art and science, and you can predict some things, but you have to also go with the flow with others).
There's absolutely no hard concrete evidence anywhere that 15x18 won't have a follow-up in continuation, and no, Jackle's purcon answer doesn't fall under that either. in my opinion.