Interesting... I honestly hadn't consider that issue (and hadn't read about that practice among the Volga Bulgars. Which four prayers did they cut it down to?
To my knowledge they diodn't remove a specific one, they removed all four and placed the other at times in the day, when it made most sense.
This was something I was considering, but I honestly wasn't sure how to work it in. Any change will likely come later with it- unless the Volga Bulgars had already done this. I was considering the eventual adoption of the tabular Islamic calendar- it has less of a yearly drift than the Hijra. Problem is, it will take a good amount of time before contact with the Islamic world brings the Ishmaeli Shi'a into contact with the Rus.
I imagine, like most handlings of the calendar in the middle ages, it will simply be dealt with in an inexact and messy manner before the High Middle Ages brings about something more reasonable. They may simply try and map Hijra dates to a more workable calendar (Muslim moveable feasts)- the Runic calendar and the Bulgar calendar are really the only candidates to map onto, however.
Honestly I think they have to move away from the lunar calendar, because it doesn't make sense in northen farming society. The harvest are based on seasons and a Ramadan falling in the harvest would spell disaster the following winter. A Ramadan in the middle of winter would make much more sense, because people doesn't work very much at that time of the year.
I had already been considering the first part- the keeping of pigs really is quite essential in Northern Russia. You'll note that I mentioned that the north was a bit more hostile to the conversion than the South. That being said, I think it will be a common case of dvoeverie- many poor farmers will raise pigs even while being nominally Muslim. They'll shirk (heh) the dietary laws in doing so. The problem is that Rus Islam will be a bit more hostile to Christians than Islam elsewhere- for reasons that will be explained. (If you'd like a hint, look up Sviatoslav's wife and speculate on the Pilgrimages.... and the fact that Novgorod's knyaz, Mstislav also has the honorific the Zealous.)
So, a pluralistic state in Northern Russia may eventually come about and may eventually reap the benefits you speak of, but it will be a long hard road there. Much more likely- in my opinion- that poor farmers will simply ignore the dietary restriction. It isn't as though people elsewhere haven't found ways to do so.
This are both interesting and quite bad news for the Islamic Rus.
Why it's interesting are because we will likely see something like a Russian version of the Yazidi evolve. Simply we will see a mix of Slavic and Norse paganism with Finnic shamanistic trait in a weak Islamic context evolve. Poor peasant isolated from the central power and lacking access to Imams, mixing their beliefs in a weak Islamic context over centuries, with the people whom doesn't follow Islamic doctrine thrieving. While this likely won't be a problem in the start, at some point Islamic purists will begin to try to purge it, and here's the problem start. These pseudo-pagans will likely thrieve and have evolve a large degree of independence from central power, so they will see this as both as a attack on their way of life and attempts to remove their freedom. Likely we will see a stubborn traditionalism evolve and the belief that they aren't Muslims.
Here's the bad news really begin, the Rus will have all the cons of having a large non-Muslim population but none of the benefits, they can't be effecient taxed, central power can't be extended over them and they will have little loyalty to the state, and the Rus Chriastians neighbours can use it as a division in Rus society, something the poor and low populated Rus will have it hard to deal with.
The good news are that these pseudo Pagans will only exist in the North Dniester and Volga watersheed, while Muslim will be the vast majority in the south (a Jewish minority will likely exist in the south). Likely urban centres will likely be the bases of Islamic culture in the north, while the country side will be mostly pseudo-Pagans.
A suggestion to a name for these pseudo-Pagans would be Slavs/Slovs (maybe with a -enians ending) to distinct themself from the urban Rus.
Of course that remind me I think we will see the Rus move faster into the Don and Volga watersheed simply because their greater focus on trade with the Persians than Greeks.