Caves as land are coming to The Lost Caverns of Ixalan and it won't be for the first time Wizards has tried to make it a thing.
Caves, as the new expansion kind of hinted at through the word 'caverns', are more of a utility land and are similar to another land subtype - deserts. Overall, caves are a bit more complex than the usual land, but will only start from this expansion. It should be noted that no previous cave cards will be retroactively be made caves as a card subtype.
There's a lot more on the nuances, but thankfully Magic helped lay all of it out.
However, this isn't the first times caves were planned as land. In fact, it nearly happened in the 2000's.
That year, a sixth color was seriously being considered as a new addition to the game. As it was being built up, it soon became clear that they needed a land type.
One proposal was cities. However, the most popular choice was (as you may have guessed) caves.
As the years went on, it was looking more and more likely that purple was going to be added. But it was kept back multiple times. It came closest in 2007 with Planar Chaos, but it just wasn't testing all that well. The balance was all off and, even though the expansion was set in an alternative timeline, purple (and by extension, caves as a viable land) were out.
As Mark Rosewater put it, "Planar Chaos was the closest we've ever come to printing a sixth color. We'd joked about a sixth color for years, but Planar Chaos seemed like an opportune time to introduce it for just one set as it only existed in the "alternate timeline." The color was purple, and the basic land associated with it was at first Cave and then City. We put it into the color wheel between blue and black. Because we were already rejiggering the color pie, we just divided everything into six parts rather than five. As purple would only exist in this set, we juiced the cards. For example, one of them was the card Mana Drain but with purple mana instead of blue. It turned out to be harder to balance than we thought and was pulling focus a little too much, so we ended up dropping it."
Caves have appeared here and there on card since such as, for example, Cave of Temptation, Cave of the Frost Dragon, and Cryptic Caves, but never as their own land subtype. They were just within the cards. But all of that changes this year with the release of The Lost Caverns of Ixalan.
The Lost Caverns of Ixalan released Nov. 17.