This is actually an intriguing thought. Would a free EW arena draw more paying customers who wanted more, or would it draw fewer paying customers because people were satisfied with free?
This might be a good idea. It will definitely give people a much better example of what online play is like than the old free 8-player did.
I think you'll get a combination of players: Some try it, love it, and want to move on to being able to participate in Events or to have access to the LW rides and will open payed subscriptions, while others will be content to continue playing in the free arena. But remember, you already have that mix with F2P business models, as well. And seeing players in the arena will draw more players to it. And speaking from experience with other MMO games, no matter what the player preferences or mechanics, it's ultimately seeing other people online that gets you to log on yourself.
Here's a hypothetical expansion on the idea:
First, have an option for a Free to Play account, no CC# required to register.
Training Arena - Available to all players, both paid subscription and Free to Play.
Early War Main Arena - Available to all players, both paid subscription and Free to Play.
Mid War Main Arena - Available to paid subscriptions. Free to Play players can "purchase" access for X number of perks, earned as normal via the EWMA.
All Other Content - Available to paid subscriptions.
Free to Play players in the Early War and Mid War arenas would otherwise receive the full content available to those arenas. All the skins, perk planes operate as normal, achievements, score, etc.