I know there have been many recent suggestions of having no-cost units etc, but I don't think it is a reasonable solution, since Stoic makes money off people that want to buy units for renown, and also because it would upset the balance of tournament play (veterans with p6 team facing off with a new player with p6 team, inflate tournament standings).
Here are some other suggestions to consider:
EDIT: AI Feature should be the priority #1 though. It provides regular games at p0-p3 which is usually non-existent, and with new players unable to get a game, it cuts the population off at its feet. Also avoids experienced players sandbagging (going to a lower level to face less experienced players) before newbies can understand the basics of the game.
1. Free Unit rotation:
Many other games employ this tactic. For each week, there are 3 random free units that everyone can try out throughout the week (one rank1, one rank2, one rank3 unit). It alternates every week. This allows new players to try out units that they won't otherwise be able to buy right away, but gives them an idea if they actually want to work towards earning that unit. It also eases the burden of reaching p6, where the majority of the games usually hovers.
2. Selling r0 units back for 1:1 ratio:
You should be able to sell r0 units back to the mead hall for full price. This allows them to try out different unit combinations without having to buy new units to do so. You want new players to be able to build their first real team without having to brunt the cost of expanding their barracks (60renown) which is much more than buying (10) and upgrading (20) units.
3. Renown boost for first 2 days:
Many games also employ this tactic. It helps beginners get over the initial grinding hump. Also gives players a taste of premium items, and if they want to continue to obtain renown boost after the trial period, they'll buy renown boost.
4. New purchasable feature: Full unlock for Custom games
This has been an idea previously suggested, all units and unit types should be accessible in custom games. This allows friends to play each other without any impediments. However, you can see how a full unlock would also not make sense for Stoic as a game studio business. Therefore, this feature should be purchasable, $5 should be well worth the convenience of trying out any team combination you want in customs. Also, new players should get a trial of this feature for the first 2 days, so they can play with friends that may have introduced them to Factions and learn the basics first before playing with real people (one of the most common complaints of beginners is no AI, because they want to practice with something to learn the game and not get owned by long-time players)