That and Alastor is canonically asexual to the point there's at least a decent sized chunk of the actual Alphabet People fandom who would go absolutely apeshit about it.
Except for the fact that asexual people can have relationships and sex...I'm not exactly sure how that works but this is the Alphabet community. The rules change all the time.
Exactly. While I've heard that Alastor has long been officially declared "asexual", I have no idea what that means to these people, pretty sure that they even have conflicting definitions. Sometimes it is said that an "ace" can be romantic and have sexual attraction, but just thinks the act of sex itself is icky. At the same time, I believe some say that an "ace" actually can be sexually active as well, which is just outright perplexing. It also seems to me that self-ascribed "aces" are contradictorily
very obsessed with sex, hence their proud place under the sex-obsessed "LGBT" umbrella.
Consider this well-known point of comparison: I take the titular character of the popular BBC show Sherlock to be the quintessential asexual character, apparently devoid of any romantic or sexual interest with either women or men. Yet at the same time, his platonic relationship with John Watson is the main theme through the entire show, spurring a
very popular non-canon gay ship among fans to such an immense degree that the show might be the foremost recipient of "queerbaiting" accusations. I'm sure many of these hardcore fujo shippers at the time are now adherent followers of the queer cult, yet it seems that they never had serious consideration for Sherlock's apparent asexuality to put aside their salacious desire to see dudes make out.
So sure, maybe Alastor is "asexual" in some fashion. But it's still possible for a relationship with Charlie to be a big part of the show such that it gives fuel to fanshipping outside of it. I'd even say that the pilot already at least gives Alastor a sense of romantic flair, given his singing and dancing with her. In response, I can certainly see angered fans slapping down the naturally-emerging Charlie/Alastor ship by pointing to Alastor's God-declared "asexuality", but I get a feeling that this angle attack is more to mask their trendy heterophobia while they instead prefer to make another gay ship between Alastor and that TV-head guy.
I just find this hanging question about Charlie and Alastor to be a particularly interesting one because this sort of ship between the female main character and the "bad boy" used to be the hottest thing among female audiences (e.g., Twilight, Fifty Shades), but now it might be considered haram.