You might need to doublecheck the legal fineprint for DMs Guild.
Content Guidelines: ‘
You cannot create content for ... personal settings, or any other D&D setting that is not specifically’ ‘Forgotten Realms’ and ‘Ravenloft’.
http://support.dmsguild.com/hc/en-us/articles/217028818-Content-Guidelines
For years now, WotC has been pushing polytheism and pushing hard.
I know that's the case, but I've seen a lot of material on there that doesn't specifically tie to either of them. Regardless, the SRD allows you to use the SRD any way you'd like, whether you post it on DMsGuild or not. Including something for sale. Or a few paragraphs on how to utilize the monotheistic PHB with the Forgotten Realms and Ravenloft. Since you want it to be setting neutral, that should suffice.
I'm still going to disagree that they are "pushing" anything, much less "pushing hard." The game is designed around polytheism, they've maintained that consistently across all editions. The three sentences in the 3.xe PHB hardly represent a change from that. The only difference at all is that more fluff of all types has worked its way into the PHB. This includes religion.
But for fun, here are a couple of searches of the 5e and 3.5e SRDs:
http://5e.d20srd.org/search.htm?q=god (5e: 6 results, 3.5e: 84 results)
http://5e.d20srd.org/search.htm?q=gods (5e: 11 results, 3.5e 103 results)
http://5e.d20srd.org/search.htm?q=deity (5e: 18 results, 3.5e 113 results)
http://5e.d20srd.org/search.htm?q=deities (5e: 18 results, 3.5e 118 results)
Assuming no overlap (and there is) that's 53 objectionable sentences in the entire 5e SRD (vs. 418 in the 3.5e SRD). Many of them are also not objectionable. For example, here are the 6 entries with the word "god" in the 5e SRD:
"Your magic and an offering put you in contact with a god or a god's servants."
"You have spent your life in the service of a temple to a specific god or pantheon of gods"
"The being must be known to you: a god, a primordial, a demon prince, or some other being of cosmic power."
"(Even half-orcs feel the lingering pull of the orc god's influence.)"
"A holy symbol is a representation of a god or pantheon."
"The GM chooses the god and associated alignment"
Of those, only one "(Even half-orcs...)" is explicitly polytheistic.
Of the other results, there is overlap and a lot of non-objectionable sentences. I only searched for a couple of deity names. St. Cuthbert comes up in one of the entries, Apollo along with a couple of other names, most that I searched didn't come up. Presumably there won't be any D&D ones because they are protected IP and not part of the SRD. If you object even to the name mythological or fantasy gods being used as examples, then you might find a few more. But it certainly is much less than even the 3.5e SRD that you say is acceptable. Hardly "pushing hard."