Steam version will require Steam always launched, isn't it?

It does not.
Steam is required to be installed and running to install SVP via Steam, but after installation Steam does not need to be running. Note that its possible to set software up so Steam is required to be running for it to work/run.

When Steam is running and you open SVP from tray, Steam will show your playing SVP to your friends. When you close the GUI(back to tray only) it will stop showing as Now Playing to your friends. This behavior can't be changed currently, maybe Valve will update Steam one day to allow users to stop software from showing as Now Playing.

Also the way SVP is licenced will also need to be modified for Steam, as full version right from install.
As the Steam client will validate if the user has a valid purchased copy.

The Steam version will have the advantage of been able to install SVP on as many PCs as they want.
The downside is you need to install Steam on each of them which can be a problem if you want to install SVP on say a work PC.
Also keep in mind Valve takes a 30%? cut of the sale price when sold on Steam.

I personally rather the non-steam version of software's as I hate how Steam shows you as Now Playing unless its a game.

There is software like that on Steam.

For example:

Borderless Gaming @ 3.99 USD
http://store.steampowered.com/app/38808 … ss_Gaming/

Source code which you can compile yourself. (Uses GNU General Public License v2.0)
https://github.com/Codeusa/Borderless-Gaming

this sounds like a plan

something like that one includes a free DLC with ffmpeg

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OK, just sent a request with a basic description.. let's see what they will answer

However, I foresee several problems:

-The SVP downloader/servers are slow enough to generate a bunch of complaints as-is.

-LOTS of people have horribly screwed up systems, which could mess up MPC (hence more negative reviews).

I think making a special "Steam Version" of SVP 4 Pro with only MPC-QT, SVPTube, and SVP Pro itself would be more prudent. MPV/QT are basically bombproof since they're standalone and have lots of fallbacks, and Valve would like the idea of a cross platform release more. Plus it would all be GNU or SVP code.

The Greenlight is closed.
And even if SVP will be accepted as a "video production content-creation software from select developer", I really doubt it will be easy to distribute all those "avisynth", "ffdshow", "python" and "vapoursynth" packages via Steam

I think it's possible to sell and distribute software with open source licences through Steam, as long as you follow the licence. I know that Civ 4 uses Python for scipting. Alternatively, the software which is distributed through Steam would just be the manager and the updating and distribution process would be similar. This is assuming that something like the Greenlight makes a comeback or SVP gets accepted as "video production content-creation software from select developer".