I'd be down for a shift in love interests.
I'm not against the current direction as a destination, but a shift of affections of different characters would be interesting for development for all involved to learn and grow from.
The age gap is huge. Even for fiction, and even for manga 13 years feels extreme between a 24 and 37 year old.
Boss girl Reina is young and her love is kind of an partially misdirected infatuation while drunk on top of a sort of seniority complex based on her own self image succeeding her late father. The biggest problem with changing that not using Ishizumi is that there is no other acceptable (not masochist boy) male character closer in age at this time that would be a good fit for her so one would have to be introduced and developed extensively before that shift could even begin to make sense and take places.
Ishizumi still hasn't shown anything really resembling love for her, IMO, just affectionate and concerned mentoring. As long as Reina needs his help, mostly emotionally right now and also in the work environment (which could be indefinite to some degree as long as they work at the same company despite her test and capable work ethic) I'm sure he will always be there for her. But at some point she won't need him as much as she does now and it just depends on how when and why.
Personally another 6 years on her would make the age gap feel less weird and that time would be adequate to legitimizing a long building relationship between these two.
On the other hand in a shorter timeframe Kurokawa gaining some confidence and pursuing Ishimzumi herself would be a fun path for both of them to experience alongside his continued support of drunk Reina, and now possibly aided by Kurokawa. It could create some unwanted triangle drama depending on how it's handled, but also double misunderstanding humour alongside emotional character growth as Reina works through that potential heartache and the other two developed their own relationship for both their sakes as well.
Didnt mean to really rant that long...
Again, not against the continued trajectory as is, just would be interesting to see it become more and different as well.