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The composting of human waste aims at three objectives. The reduction in volume of the waste, the reduction in the “yuk” factor and the reduction in health risk.

One problem is when the waste looks composted but still has hidden dangers - often due to eggs rather than bacteria. It is also worth considering the whole sanitation chain. It’s a waste treating waste to a high level then putting it on a polluted field or where the crops are exposed to contamination later - e.g during transport or at the market. Have a look at...

https://wedc-knowledge.lboro.ac.uk/details.html?id=16289

On the subject of cold weather, others have given good options, so I won’t repeat them, but I will give some other, wider factors to consider. There is also the issue of final disposal. In very cold climates, arable agriculture may be limited, so there may be limited opportunities for re-use, so don’t follow the route and then find all the compost is just dumped. Timing of field application is also limited, so if there is only one opportunity- e.g. before sowing, then the waste will have to stored for a year anyway and faster composting may not be a limiting factor.

There are insulated compost bins on the market but they are very pricey and, as mentioned elsewhere, the compost needs the correct c:N ratio, so the material will be bulked out, increasing volumes. Larger, centralised composting will increase temperatures but increase the exposure to disease due to handling and transport. One positive thing is that frozen shit is probably easier to deal with than the same material in the summer!