I believe Trumpeter announced an IS-4, so maybe they are also planning one? Nothing to base my hypothesis on, except that the IS-4 was part of the lineage that included Project 279.
For such a niche subject (how many real ones were made, one?), to have three kits announced is a good thing for the consumer. There are those who buy the first one out of the chute, but others will wait until the "experts" have spoken. For myself, Panda put out a pretty nice "Tunguska" air defense system, so I might be in the first group. Will Takom and Amusing Hobby drop their kits, now that Panda's release seems imminent? No one knows for sure.
But one thing I do know is that there are a heck of a lot of other subjects that have not been done yet, so we win either way! Well, assuming the kit makers choose to do them. Now will someone please push out a T-10?