Languages: Lots of Javascript (maybe more Typescript, but would be shocked if that had taken over completely). Probably quite a bit of Python, Ruby, Go, PHP. I'd be pretty shocked if something we haven't already heard of gains a big market share in five years. New languages are a slow-burn thing today. One plausible shift would be Rust edging out C/C++ in lower-level application/library development. But will be a slow transition, as a fraction of total code written, it'll still be quite small.

Stacks: I suspect we'll see more emphasis on making new-built software that can be sold to management as "cloud aware". Which in practice, probably translates to more Kubernetes. But again, mostly stuff we're seeing today.

Hardware: amd64 still dominant for servers and desktops. ARM for mobile, gradually making some inroads into the server space (but if it takes over completely, that's still >5 years off). Maybe some ARM desktops. Hopefully POWER will be hanging in there, and maybe some RISC-V hardware -- but only in niches. Number of cores will continue to increase, but addressable RAM and memory bandwidth will be even bigger limiting factors than they are today.

What are they developing?: Line-of-business CRUD apps.

Edit: Re-reading, this comes across as quite negative. I do think we'll see a whole lot of innovation in these areas -- just that it'll take multiple years to filter through to what the average developer is working on.