the Abandoned tag is an automatic thing on F95, any game that doesn't get a direct update on the game is labled as such, so you should read abandoned more as a "Lack of updates" label, doesn't matter if the dev actively shows they are working on something.
now the thing with Kenko is, that he is a Perfectionist, he won't say shit until it's done and ready to ship, he doesn't seem like the type of guy who would give us monthly Demos, plus, he said somewhere that he doesn't want to spoil the surprise of us going "Oh cool, he added THAT monster!"
the illustrations you see are more for his book-series he keeps working on since 2007, so those are his more recent additions, but he is thinking of adding even those one day to the game.
as for the Cowgirl/Holstaur, she isn't in the Demo, but as you can see, her and the Alraune got most stuff done, willing to bet Kenko is already working on other monstergirls for the RPG if i may sound optimistic here. usually i don't give devs this leeway, but the dude is working on his IP for a damn long time, so i trust him. even if the wait is excruciatingly long.