From a rules perspective, I don’t see the storm shield guys replacing DWK. Apart from being clearly geared towards combat, they likely (important caveat, as we don’t know the rules yet) will fill different roles.
DWK have four key strengths:
1. Massive damage output
2. Built in delivery system
Assuming they can be given the Inner Circle stratagem, so will they. And before you bring up the point that you pay 1CP - note the CP system restructure happening.
3. Synergy with Ravenwing (to enhance delivery system)
See above. Combined assault relies on the Deathwing Keyword, which means anything that has that keyword, can drop in with Ravenwing. Which leads to me to believe there could be more units besides the DWK that can benefit from it while giving similar damage output.
4. Pretty survivable
They have the same amount of wounds - assuming it follows the intercessor stat-line. Probably a 3+ armor save, and a 3+ invuln with shields. They are pretty comparable.
Who knows what exactly these guys will do, but to directly compare them
1. Power swords will not equal mace of redemption damage. Shooting is nice, but not really in the same ballpark - if you’re taking DWK, it’s to delete units in a single turn of combat, which I can’t see these guys doing
They are comparable to Company Veterans - which means they will get access to extra weaponry such as Chainswords, or the primaris version of a thunder hammer (whatever that may be). They are comparable, by that logic. Which reminds me, they said chainswords are back, which if I were to read at it deeply, implies they are buffing them?
2. Most likely won’t have an inherent delivery system like deep strike. Which means taking an expensive transport to get them up the board
See previous point.
3. Very unlikely. Without massive changes, combined assault won’t work (although the need for it is lessened by taking the transport these guys will need)
See previous point as well.
4. Clearly they’ve got stormshields, and I wouldn’t be surprised if they have artificer armour if they fill a veteran/honour guard role, so most likely will be comparable to deathwing knights in having 2W, 2+/3++. But, DWK can also benefit from their relic banner and fortress of shields. Maybe the new guys will get something similar, but maybe not.
Primaris Ancient and a maybe a primaris drop-pod springs to mind. I am still under the impression everything the firstborn has will be replaced, and true to your 1;1 analogy, made better. And there is always a possibility that the pennant of remembrance can be transferred over to the primaris ones, in a few years time, if it hasn't been superseeded by anything.
Conclusion: these units are different. I can see some people taking them instead of DWK, but they’re not a 1:1 replacement - both units require list building around them to make them shine, but they will require different units in support to achieve those synergies
Forgive me, but I disagree. If the Assault Intercessors are Company Veterans, then how are they anything but? Their loadout (at least ones we seen) are the same. The function is also the same.