I wonder if it's possible to welcome an existing Hollow-oriented spirit - like, say, an Arrancar - into one's Spirit World/Inner Soul/whatever-you-wanna-call it, as a sort of mutually agreed on Hollow infection/parasitism/symbiosis with a Shinigami. Face value it sounds like an absurd question, but what even is an Arrancar/Hollowfication of a Shinigami, if not (in both cases) the injection of Hollow-oriented spiritual energy into the Shinigami's Zanpakuto & soul? Sure the details are different, but it seems like the root of each dealio's the same. And souls are explicitly, demonstrably flexible and able to rise to meet that which is demanded of them, if they're pushed the 'right' way. Per all that it seems to at least be possible to do, regardless of the practical challenges and general difficulty in execution.
And per that... I wonder if we could bribe Sandwich into chillaxing in Ichigo's soul faffing about chatting with Zangetsu and eating Spiritual Food, so that we can deploy the true Power of Friendship (summoning allies that are maybe stronger than us to help us gang up on challenges) when in dire straits. Or any sapient Hollow, really. And before people cry 'due cause for death', let's not forget how (A) Soul Society did re-accept several of its Visored former members, and (B) There was that whole reference to the amoral, whatever-means-achieve-our-goals, band of killers style old Gotei 13. That, on top of how permissive the current Gotei 13 is about eccentricities, quirks and general 'soft' rule breaking from its VIP members (Mayuri and Kenpachi both should really not actually still be in their positions, in a more conventionally strict military unit). Between those three points, seems like there's canonical precedent for allowing highly atypical stuff both historically and currently, as well as reason to believe they're at least open to making new allowances in the modern day.
So while I'd still agree that yeah, Ichigo Hollowfying/getting a Hollow soul-roomie/etc. would be a big old red flag for the guy and there might even be a trial over it, barring Aizen intervention I feel like there's a good chance it'd all work out. A chance at getting the superweapon problems in Hueco Mundo that prevent Soul Society from having a stronger/more oppressive presence there, potentially allowing themselves to be placed in Shinigami souls? Sounds like a great way to take the, absent Fullbringer antagonist groups/Aizen's rebellion/Ywach leading the Quincy, biggest threat Soul Society has to account for, and blunt its fangs. That seems like the sort of thing Central 46'd be all about, IMO.
And if Aizen cocks it all up with Suigetsu and Ichigo's slated for execution? Then we roll with it and play it by ear - it certainly wouldn't be an unexciting direction for the plot to take, if the worst case happened. And, silver lining; souls grow and evolve their absolute fastest when put under incredible, life or death pressure pretty much exactly like this hypothetical scenario would offer.