As someone working on TIBCO BusinessWorks, a competitor/alternative to webMethods, this sounds all too familiar. We have had major challenge ourselves in bridging this gap - semantic diff/merge on process/flow engines like BW, WM, etc. with visual tooling.

Typically developers care about this, business buyers don't and they direct budgets and in many ways, product prioritization. To a large extent the proprietary or obscure nature of integration DSLs never helped bootstrap any meaningful tooling for users.

That's changing though with developer-power driving prioritization and investment. In our case, we hope to make good progress with an upcoming project called Flogo. Currently in stealth and soon to be OSS.

Disclaimer: I work at TIBCO on integration