2 religions isn't all that hard on Monarch with a decent number of opponents (6-8), though you do need to be focused with your tech plan. I can only assume that it will be even easier with 7 religions in the game instead of the prior 5. You focus on an early/late combo. As long as you don't adopt a civic that causes unhappiness for competing religions, you're fine.
If I'm planning a 2-religion strategy, it's usually Runes + Order. Runes is so all-purpose that it's just nice to have - money and earth mana. Order is down the religion path as it is, and you'll want to take advantage of disciples so it makes sense to head that way.
I think that with Empyrean and Esus there are some new possible combos but I haven't looked over the revised tech tree in too much detail yet. For example, if Runes (for money) + Esus (for something to spend it on) is possible, that would be a nice combo.
If you turtle up and found a single non-capital, food/production city, you can pick up Runes and a second religion in the same city. Expand after that. Found the shrines and the Bazaar of Mammon multiplies both. Obviously, that doesn't work if one of the shrines doesn't produce money. If you're planning that, you need to plan for them to be founded in different cities so you can build different multipliers.
Also obvious, I suppose, is that you can't do this if you plan on a religious domination strategy. The point of having 2 religions is to spread them and use both. That will dilute a religion strat (unless you're trying to fund them to keep them from spreading - darn hard on higher levels).
