The only really clean path between VOLT's .vtp project and .fea code would be scripted, i.e. something that parses the plain text of the .vtp file and converts to .fea syntax. I am not aware of such a script, but have considered commissioning one several times.
In the meantime, you could also experiment with opening the compiled TTF in DTL OTMaster and then use the export .fea option. I've not tested this workflow, but its another option along the lines of those you've already tried, and might produce better results.
I do design typefaces too. I'm not saying it's not important to protect the thing we do. I have seen a couple of times that the exact unique thing one of my typefaces had had been distorted.
Oh, I've seen my Gabriola typeface fake bold more times that I've seen it displayed as intended; also obliqued, stretched, squished, rendered in neon — okay, so that was pretty cool! —, and amateurishly handpainted.
Please help me understand this: If the concern is about the quality, so how about the time that there isn't a modified font and instead the designer did the modifications to the text written by the font (as in a typographic poster)? Are we going to be concerned about that as well? I mean I'm a graphic designer and it is safe to say that I never use a font without doing some changes to the text.
You understand that there's a difference between doing typography and font manufacture?
I'm not sure what kind of 'changes to the text' you are talking about here. If you mean, e.g. tracking or other adjustments to default spacing, or applying different colours, then you're simply doing the kind of things with fonts that fonts are designed to enable, you're doing typography. I might not like your typographic choices, but that's what the existence and the licensing of the font are created for.
If you're talking about converting text to outlines and modifying the appearance of the text by editing those outlines, then you're creating a piece of modified text, not a modified font. Again, I might not like what you do to the text, but unless I'm going to explicitly prohibit such a use in the license agreement, I accept that when you convert the text to outlines you are no longer dealing with my font — indeed no longer deatling with text — but with an image of text.
If, on the other hand, you decompile my font in an editing tool, make modifications to some glyphs, maybe add some glyphs, and adjust some spacing, there are a lot of things in that process that can affect the quality not only of the things you are consciously modifying but elsewhere in the functionality of the font, as unintended consequences. When decompiling a font and making a new, derivative font, you're not editing text or an image of text that you made, but are changing the thing that I made. So I think I have a right to be concerned about the quality of that thing, for its own sake.
[Note that this is not to say that we're going to disallow modification. As I wrote above, this is something we're considering as we draft our commercial EULA. But my inclination is that I'd like to know who is doing what to the things that I make, so that I can have some input of making modified, derivative fonts as good as they can be.]
We're still considering whether or under what conditions to permit modification in our commercial license. What I've done in the past, in some of our no-fee no-commercial-use licenses, e.g. for the SBL fonts, is to include a requirement that any modified fonts be sent to us, and we reserve the right to include such modifications in future versions of the font. The context there is fonts for specialist scholarship, recognising that modifications, especially extensions, might be useful for others in the user community. But I think there's a more general point to be made about who owns derivative works, and the right to exploit those commercially. Modified fonts are covered, as derivative works, by the copyright of the original, and by the terms of the original license agreement. That is, no matter how substantially modified, the fonts belong to the original copyright holder.
I've seen modified versions of fonts used in branding, in which changes to a few common letter shapes create a distinctive typographic look and feel without the expense of commissioning a whole custom typeface. My understanding is that there is nothing in that case to prevent the original font foundry from releasing their own version of that modified font — even taking that modified font as is and releasing it, or licensing it to another customer, even one in competition with the branding agency's client — and thereby undermining the value of the branding exercise.