Lambda the Ultimate

Suppose you want to type-check a message protocol, or a stream grammar, or partially ordered datagram exchange. The type signature might be declared in advance, or you might be told at runtime during negotiation.

What kind of type declarations comprehensible to average practitioners can work well enough without a lot of training or priesthood snake-oil? I ask because sometimes I see type expertise languishing in what looks like a backwater from my view. I want to type process pipelines, stream flows, crypto exchanges, and connection protocols.

I only ask to see if interesting ideas come up. A side channel in rumination recently was about static analysis of what might happen if shell command lines were executed, given sufficient meta-info declarations about dataflow behavior. I thought a developer might be interested in tool support for analysis of what happens given components that interact with specified finite state machines and message formats, etc. You can elaborate the idea further from there.

New abstract creative reasoning is what I'd like most, rather than existing work -- which I would expect to be narrow, concrete, unimaginative, and grinding in application. Of course I don't mind being contradicted with beautiful work.