Should you ever care to compare the systems listed for the frigate in the RFP with the equipment on an LCS, and in any of the modules, you will see they are both pretty nearly identical, and further, most all the major systems being used for the frigate were developed in the LCS program. COMBATASS, NSM, SeaRam, Mk 46 gun, Mk 110 gun, Hellfires, Fire Scouts, the variable depth sonar to be used, and so forth. The frigate will have a different hull, and a 32 cell MK 41 VLS of unstated length (but all I have ever read that it will fire is Standard missiles and ESSM, making it tactical length.) It will also have "beefier" electronics, but most of those are planned as upgrades for the LCS, including a better air search radar, and the SEWIP light ECM system and Nulka decoys.
This is being done for commonality reasons, for both easier logistics, and training. If the systems everyone claims are crap on the LCS, then they will be crap on the new frigate...it is using the self same systems. And if they had not undergone all their teething troubles in the LCS program, they would not be the currently working systems "off the shelf" for the frigate program to use.
As far as LCS being put into reserve... The total force requirements for the US Navy call for 55 Small Surface Combatants. There will be 20 frigates, and 35 LCS. If more frigates are constructed beyond the 20 currently planned, the Navy has stated they would be in place of greater numbers of the still-in-planning Large Surface Combatant. As long as the Navy remains committed to the 355 ship goal, and as long as funding for the new ballistic missile subs eats up half the ship building budget, it is a pipe dream to think that the Navy will drop 35 newly built vessels in favor of more numbers of more expensive frigates. The reason the frigate numbers would increase--to replace Large Surface Combatants--is because they are cheaper than those ships. Most stuff I am reading is saying that funding of a 355 ship fleet is pretty troubled. Dumping 35 new ships to buy something else more costly won't make those troubles reduce.
And further... Lockheed has ALWAYS claimed they could put strike length VLS on their LCS version, and at this year's show in January, they had a model out with 8 MK 41 VLS cells. 4 of those were strike length. Lockheed said they were in talks with the Navy about it, and I read that the program is indeed considering adding them. True, it will depend on funding, and I am not holding my breath. But, if they can convince enough key congressmen of the logic/value of paying to put that feature on them, then it is not in the realm of the impossible that one day there could be LCS firing some Tomahawks. AND...that might also actually be more than the frigates can do...
Time will tell. I expect that--after the winning frigate design is announced this coming Sumner--we MIGHT finally be told what length the VLS system will be (??)