Blender is rapidly becoming really powerful for many 3d workflows. Would it be legaly possible to make an houdini engine integration? I for one would really like to use HDAs inside blender instead of exporting static geo.

Houdini Engine for Blender would be awesome.

I do not think that would work as Blender plugins needs to be under GPL license.

There's got to be a legal workaround since companies like OTOY are doing it, and I'm pretty sure their code is not GPL.

OTOYs workaround is to maintain their own customized Blender build which provides a network socket connection to link to the OctaneServer software which runs on the same machine. OctaneBlender passes the scene data to OctaneServer over this socket and the rendered image returns to blender the same way. The Octane Blender build is GPL, the Octane server where all the rendering code lives is not. You cannot use octane with vanilla blender.

I don't imagine SideFX really wants to maintain a customized version of a another 3d application.

Thats not the problem!
Houdini engine uses thrift for intercommunication so it's a server / client setup.
I think otoy/octane has the problem that blender hasn't got a solid api for 3rd party render engine that are closed source.

The simplest way would be to use a python/thrift setup. But it would be not a fast solution.

As long as the plugin is GPL compliment(as it ideally links statically to blender) I don't think there's an issue. Houdini engine plug ins are linked dynamically(to Houdini), the same way Blender links to the OS.

Has there been any official/sesi talks about a Blender integration for HDAs? Like “never” or “maybe” or “yes it so coming” “it is not possible”?

Using HDAs in Blender with EEVEE for really rapid design work, especially for concept art, would be very very awesome. Right now I use gltf for models and that works ok but being able to use HDAs would enable quite powerful workflows quite similar to what you can do in Unreal and Unity but with more artist friedly tools.

anyone is free to develop HEngine integration for any host app
https://www.sidefx.com/docs/hengine/_h_a_p_i__overview.html [www.sidefx.com]

so you may try asking on blender forums too and I bet that if there is an interest the blender contributors can make it happen faster than waiting for sidefx

I took a look there and there is no documentation for doing this except for on Windows as far as I can tell. (I'm on mac)
I guess there is ways to decipher this but it will take a lot of time. Just for fun I tried to get a basic basic test running but it is not straighforward even if the API itself seems easy enough. Anyway, even if I get something running I will not have the time to make this meaningful so I guess I will wait for someone else with a burning desire to make this happen

houdini engine in blender can be amazing for many things
would love to do it but sadly not in my skills…

https://github.com/eliemichel/HoudiniEngineForBlender [github.com]

https://devtalk.blender.org/t/open-mesh-effect-branch-prev-houdini-engine-modifier-for-blender/8218 [devtalk.blender.org]

Élie Michel posted this recently, for Siggraph2019:
https://blog.exppad.com/article/the-need-for-open-mesh-effect [blog.exppad.com]