Dear Mark, your said "Adventures - not remotely parasitic". Please. Inkeeper? Lucky Clover? And this could be applied to most of the supposedly "non-parasitic mechanics". Little matters if the mechanic is not parasitic per se, if later we need to play the usual "pre-conceived deck" to compete. This kind of design hampers creativity and freedom in deckbuilding. I don't like it.

You are confused about how parasitism works. Cycling is a very non-parasitic mechanic. You can easily throw a cycling card in any deck with full mechanical utility. But Astral Slide and Lightning Rift, as well as many other cards, exist. Those cards encourage you to play a lot of cycling cards in one deck, but it doesn’t make the mechanic parasitic. Yes, we’ll make cards that encourage you to play a lot of the same mechanic in a deck, and that might even be a tournament-viable strategy. None of that makes a mechanic parasitic though. You might be arguing that you don’t like cards that encourage a player to put a lot of the same mechanic in one deck, but those types of cards are, on average, very popular. So, I’m not sure what I can say to assuage you. You dislike something that a lot of players enjoy. Luckily, there are plenty of non-linear tournament-viable strategies available. I would try focusing on those.

will we ever get to see cycling cards / cycling-matters (astral slide/lightning rift) again?

Cycling is too good a mechanic for us to never use again.

For a set about closing rifts, why weren't there any rifts in Time Spiral?

It was a temporal disaster which meant many rifts appeared in Dominaria’s past. For example, Lightning Rift in Onslaught. : )