I am seeing more and more users wanting to implement end-to-end connectivity from GW to service mesh. Particularly when it comes to Kong, we have done all the heavy lifting in Kong[1] + Kuma[2] (the latter a CNCF project) to do that.
Typically we want to create a service mesh overlay across our applications and their services - to secure and observe the underlying service traffic - and still expose a subset of those via an API GW (and via an Ingress Controller) at the edge, to either mobile applications or an ecosystem of partners (where a sidecar pattern model is not feasible).
With Kuma and its "gateway" data plane proxy mode, this can be easily achieved via the Kong Ingress Controller, which is mentioned in this spreadsheet.
Disclaimer: I am a maintainer of both Kong and Kuma.