I think it's far more likely for PLC programming software to be embedded in the PLC itself in the future than for the manufacturers to switch to Linux. I don't know whether it would be a remote desktop/VNC type solution, or something more like HTML5, but that's the direction I see things moving. The major manufacturers store pretty much the full project in the PLC already, and lord knows that just about every AB programmer already makes the majority of his changes online.
Do I want linux support? of course I do. But for goodness sakes, lots of major manufacturers don't even support Win 10 yet, let alone anything out of the box. It isn't happening any time soon.
It all comes down to cost. Do you want the cost of the programming software bundled into the PLC, or separate? How much support is the software developer willing to throw at "other" platforms. OEMs, Integrators, and End users all have different expectations of those things.