Yeah, TASM is coming back as a software upgrade instead of a separate missile. TASM's reason for existence was retired, i.e. it was deployed specifically to sink Kirov battlecruisers, which analysts decided had enough armor to require Tomahawk's larger warhead. When the Russians retired the last Kirov (along with much of the Soviet fleet), the US didn't see any reason to keep TASM around. The remaining inventory was converted to TLAM-C to replace missiles expended on ground targets in Iraq.
Now the Russians have reactivated a Kirov and plan to refurbish (maybe) two more, so I guess that's the reason for the upgrade.
I talked to a Navy Cmdr in the late '90s as Harpoon was being withdrawn from submarines, and he said the big problem with sub-launched anti-ship missiles is the range at which they're safe to launch is farther than the sub can reliably identify targets. Nobody wants to be his generation's Fritz-Julius Lemp.
The US is developing a stealthy anti-ship missile (AGM-158C LRASM) with a lot of gee-whiz technology like autonomous ship identification and in-flight satellite data links. Right now it's only air and ship launched, and they're still trying to decide whether to deploy it to subs.
https://en.wikipedia.org/wiki/AGM-158C_LRASM