FTP does not automatically make the game popular and with great online. Man of War 2: Arena is an attempt at FTP which failed because the FTP mechanics are not suitable for RTS. And the old Man of War 2 still has stable online.
Stop fixing what isn't broken.
Also Relic tried that already with CoH Online
and tried to appease MoBA people with DoW 3
Both horrible fails, gameplay- and businesswise