Personally I’m not a big fan of allowing closed source plugins if there will be a source provided option at all - if there are, we end up with the same drawbacks of other systems, where functionality goes largely unmaintained, and plugins die and drop off the map quite often. And while I’m sure there would be a decent amount of both types, it kind of makes the distinction a bit useless.
That said I understand peoples’ position, though I’d be fine with even something like no closed source plugins, but closed source plugins may be featured in the marketplace from time to time or some such.
Closing the source for a static library brings its own issues - namely a debugging headache if anything should fail inside the library, and in turn, a support headache for the author to figure out what happened. It also largely presents the same drawbacks as entirely closed source plugins (minus engine-integration maintenance, which is good), namely that the can go unmaintained and thus die off quite quickly.
The other thing is that providing source makes it a lot easier to have a community maintained support pipeline, which any developer of middleware knows is the biggest source of time spent not developing your actual product. With a closed source product, you are pretty much on the hook to provide close in support no matter what.
I still think those that want to keep their source closed would do just fine selling outside the marketplace. If your source is the result of years of R&D, sure, keep it closed. But by that same token, your advanced code should be enough of a draw that the should sell itself. If it’s really that good.
Further, I’d prefer not to use closed source plugins just because I may need to integrate that system with others the author(s) never knew about, and there is zero of that happening with multiple closed source plugins. So it’s a real turn off in terms of wanting to buy a if there’s no source, because I know
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support will be a hassle no matter what, even if the author is attentive,
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I can’t debug it myself,
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I can’t integrate it with other systems if need be,
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I don’t know if the author will even be around in a year, or if the will survive, and I won’t be able to update it.
Just my two cents.
Edit: Also, source provided/available is a lot different than open source, and I think that’s what we’re all talking about here (source provided, not open source as in FOSS licenses and such).