Nirth: That would be an unnecessary strain on GOG's resources, at least for now. I think it's better if they continue to focus on windows and secondly mac and maybe linux in the future.
I wouldn't mind GOG offering Android versions of those indie games where e.g. Humble Indie Bundles offer them too. Spacechem, Anomaly Warzone Earth etc. They'd still sit well into GOGs prime directives, like "Uphold the DRM-free law". I'm unsure how much extra hassle giving out the Android versions does it cause to Humble Indie Bundle.
But for making Android "ports" of PC-only (DOS) games... maybe not, at least for now.
Nirth: As for the site I would love an optimized mobile version.
Seconded. No need for a mobile GOG app, as long as these pages would work better with mobile devices, a separate mobile version of them if needed. At least for me e.g. the floating menus cause a bit of problem with touchscreen devices, also the pages are maybe a bit too wide for smaller screens etc.