In Russia there are plenty of new options like Kazan for example. In Czechia Brno or perhaps Plzeň. As for countries that haven't hosted recently there would also be possibilities like Great Britain or Norway. Personally I would favor giving a Division I country the opportunity once in a decade.
If Russia had attendance problems last time, I'm not sure Kazan would be such a great idea.
In the Czech Republic there are also good reasons for it not to be in other cities, and those concern infrastructure. Amount of seating is obviously a main concern, but for a tournament of this size other facilities are also required, and they must be sufficiently modern, or the arena must be specially modernised for the purpose of hosting. O2 arena in Prague was built with this function in mind. Ostravar arena was also renovated with an eye to being able to fulfil this function. Brno only has a capacity of 7700, Plzeň has a capacity of 8236 but was built in 1950 and a quarter of that is standing. Pardubice for example has a capacity of 10194, but again one fifth of that is standing room and it was last renovated in 2001, I'm not sure it can provide the other facilities necessary for an event of this size. Ease of access is another matter, you need an international airport. Pardubice does have an airport with a new terminal built recently with the aim of being a kind of "cheaper Prague airport", but honestly if two cities in the country are going to be hosting, you need to put one in Moravia and not so close to Prague. And with the infrastructure Prague has, you can't sensibly leave it out.