Not if you have 10,000 anti-artillery 100KW laser on vehicles. Let's say each one costs 1 million dollars, you would have to spend 10 billion dollars. Lets' say your operating costs are 3 billion a year (2 man crew at total cost of $100,000 each and another $100,000 for support, maintenance, and command, per unit). Over ten years the system would then cost 40 billion dollars, ($10B upfront + $3B/year x 10 years). This averages out to 4 billion a year. Per wikipedia, there are 25 million people in Seoul metropolitan area. This turns out to be $160/per person per year (or 43 cents per day per person).

You can bet the US government and the South Korean government are going to look seriously at that option.

I imagine any rotational speed beyond a certain point is indistinguishable from other, higher rotational speeds in that you are basically heating the whole shell. I don't know how fast these shells rotate, but it seems like it would be hast enough that they are probably heating the whole shell anyway.

Additionally, if you are firing from close to the intended target, you may not have to deal with rotation at all.

This could be countered somewhat if you targeted the front end of the mortar.

They don't stop you from getting hit the first time, though.