Historically speaking, memes adapt to match their format, and meme formats adapt to match whatever losers have at their disposal. Think of the rise of short, Vine-like video content (which is why r/YoutubeHaiku and TikTok always has useable content). Right now memes are mostly template-based exploitables that are easy to mix and match; this explains why r/MemeEconomy has much of its discussion centred around new templates or formats – especially those that are remixable (BongoCat and Expanding Brain are good examples).
Granted, memes don't have to fit under these categories. Bowsette was a pretty vanilla art trend that happened to kick off because of a popular Tweet. The Storm Area 51 meme was similar, albiet real-world. These kinds of things usually start off strong and slowly fade – remember planking ? They're popular and noteworthy, but rarely change the "meme landscape", as you're calling it.
So to answer your question, the biggest change to memes pretty much has to be a change in popular meme formats. Imagine if any of the following were to happen:
- Twitter/Facebook suddenly decline, or are taken down (no more repostable image memes/reply chains/social media banter)
- 4chan disppears (no more greentext/vapid internal circlejerking)
- Reddit makes a dumb decision about meme subreddits/policy (not hard to imagine)
- Some new social media platform suddenly gets popular
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Copyright law changes lmao