I've been researching going to electric brewing. When it comes to efficiency, there's no contest. Electric (we're talking immersion elements here) is far and away less costly than gas, and all of the other issues involved in using gas indoors go away, too.
The drawbacks, dealing with the minor first, is that in most cases, a wiring job is going to be involved to run a 240VAC circuit (30A minimum) to the brewing location. It is of course possible do this yourself, keeping in mind that DIY work with electricity is very unforgiving, to the point of being lethal.
The really major drawback to electric brewing, though, is in controls. I should note that I exclude from this discussion the various electric "heatsticks" which are used either for auxiliary or as the sole source of heat. I have multiple reasons for doing this, which are not germane here and now.
For me, electric brewing must incorporate permanently fixed electric elements in the brewing vessel(s), which elements are temperature / time controlled, thus automating all the steps from heating the strike water through lautering. The problem with any given electric element is that it can't be adjusted like a gas flame. It is either on completely, or it is off. For an effective brewing setup (I think the best known on this forum is Kai's Electric Brewery), the controls maintain the proper temperature by automatically switching the element(s) on and off automatically.
If it weren't for the controls, electric brewing could be set up fairly cheaply. As it is, a full-blown set of controls (taking the commercially produced version of Kai's controls as an example) cost several thousand dollars. This, when added to the rest of the cost of the electric brewhouse, means that even DIY, it's pretty pricey.
The most ingenious approach I've seen to electric brewing thus far is the Speidels Braumeister (you can do searches, and there are several YT videos), and it still comes in at $2500 - $3500, depending on whether the 20l or 50l version is desired.