I don't know why the writers are hinting towards Nandor having romantic interest in The Guide but honestly, I'm not too worried.
May I remind you that Nandor has a pattern of romanticizing people and briefly settling in toxic relationships when he is lonely and depressed.
- He liked Meg simply because she gave him good customer service.
- He adored Gail who strung him along for decades and tossed him aside like he was nothing as soon as she was turned.
- He joined a cult and slept with Jan who was manipulating and brainwashing him when he was most vulnerable and emotionally unstable.
- He selected Marwa to marry because she was the wife that least threatened his ego and then wished her to have zero free will, changed her personality and transformed her into an entirely new person.
- He became obsessed with Freddie simply because he was Guillermo's boyfriend and since he was miserable in his own relationship, he sabotaged Guillermo's relationship.
My point is Nandor's coping mechanism for his eternal loneliness and losing Guillermo is seeking out shallow relationships. We only have 5 episodes left and the writers must be planting seeds for a reason. I just can't imagine the writers being this careless and pairing Nandor with The Guide last minute. Keep in mind, the writers were green lit for seasons 5 and 6 at the same time. If they were really going to scrap Nandermo and push Nandor and The Guide, then it would have made more sense to plant seeds of a budding relationship between the two at the beginning of season 5. So why now?
As much as I like The Guide and Kristen Schaal, her character has always been a plot device. In my opinion, her entire story arch in season 5 was for the writers to have a reason as to why Nandor would be in a cage when Guillermo confesses to betraying him. Nandor needed to be restrained somehow in that moment to prevent him from killing Guillermo right then and there.
My prediction is that if Nandor makes a move on The Guide then she will be the one to call him out for only showing interest in her because he's lonely. I'd like to think that The Guide has enough self-respect to not reciprocate (I admit that I haven't watched 6x06 yet) since he was so aloof and rude to her all last season and barely had any memorable or meaningful interactions with her in earlier seasons. Maybe if Nandor is called out, he'll realize the error of his ways and admit that what he truly wants is Guillermo.