Why This Works
The beer margarita sounds like a novelty until you have one on a hot day. The lager stretches the margarita into something longer and more sessionable, and the lime ties it all together.
Alcohol-free tequila brings the agave backbone so the drink reads as a margarita, not just a limey beer. Without it you have a shandy; with it you have a cocktail.
Keep the limeade tart. The beer adds a little sweetness of its own, so a sharp lime base keeps the whole thing balanced.
The Alcohol-Free Swap
You need both a good non-alcoholic lager and an alcohol-free tequila with real agave character. The beer lengthens the drink; the tequila gives it identity.