Why would it be the only nuclear-powered cruiser?
Peter the Great isn't going anywhere.
I think he is referring to the fact that they will likely replace the old reactor combined with boilers to super heat steam to drive the gas turbine propulsion with newer more powerful nuclear reactors developed for new carriers that should greatly improve performance with a far more compact design.
Until Peter the Great goes through a similar upgrade it will be the only nuclear only powered Russian cruiser.
Just focussing on the armament:
Main weapons strike: 20 P-700 Granit supersonic long range anti ship missiles
Air defence: Long range: S-300F launchers with 96 missiles (Peter the great has S-300FM)
Short range: 2 x Osa-MA launchers with about 20 missiles each replaced with TOR
Anti Sub: SS-N-14 with anti sub and anti ship capability.
RBU rocket launchers firing anti sub rockets, anti diver rockets and anti torpedo rockets replaced with SS-N-15.
10 x 21 inch torpedo/missile tubes able to launch torpedoes or SS-N-15 ASW missiles (later replaced the SS-N-14).
Gun armament: 2 single barrel 100mm gun turrets replaced by two twin 130mm gun turrets.
8 x 30mm gatling mounts later with Kashtan added.
Likely upgrades will replace the SS-N-15, SS-N-14, and SS-N-19 with UKSK launch bins for a likely total of about 80 missiles. The SAMs will likely have the Rif and Rif-M replaced with Redut, TOR replaced with upgraded TOR, 30mm gatling guns replaced with Duet turrets and Kashtan replaced with Pantsir-S1. RBU rockets will likely be replaced with PAKET, and the main gun armament will likely be twin barrel 152mm Koaltion guns or possibly bigger guns of 203mm calibre.
New electronics and a revision of the radar suite fitted and it should be a very capable ship.