As an EV driver who uses Airbnb frequently and has hosted people also, I'd like to chime in on this.
1) Offering EV charging is a fantastic incentive to attract guests. During this period of time when national charging infrastructure is still in its infancy, EV drivers going on holiday will look at a handful of apps (Plugshare etc) to see where they can charge on route and at their destination. If you offer charging you will stand out on these maps, I can guarantee it. The piece of mind knowing that your accommodation has a charging option will definitely make the difference between one accommodation and another when choosing where to stay. I'm not suggesting to offer free charging, just some form of charging.
2) There is no danger plugging an electric vehicle into your house. The chargers provided with the cars are completely safe and only draw a very slow charge. For zero investment on your behalf, you can even just allow drivers to plug into a normal wall socket, just like an electric heater. Only the most off grid battery powered property would need to worry about the demand on their circuit. (Most people in those types of situations have a good understanding of their power generation anyway). If you want to offer a better service, you can have an EV charger installed to provide faster charging. These are getting cheaper and cheaper and have in built timers and even payment methods included.
3) The cost. Nobody is suggesting not to charge clients for the electricity they use for their cars, however this would be a great and fairly cheap bit of marketing for your property if you did. Most normal guests won't think twice about leaving heaters, AC, TVs on consuming your electricity. On the other hand, due to the nature of owning and electric vehicle, most owners are very conscious about their electricity consumption. The cars don't actually use that much in the grand scheme of things, but the owner will be able to tell you how many KWhs they use, and if you simply know your electricity cost per KWh (check your last bill) then it's a 10 second calculation to know how much they owe you. You can even put the $/KWh on your ad post to let people know in advance. Failing that, to keep in very simple, most people are happy to pay 15$AUD which will cover most full charges. Generally people don't ever need to fully charge anyway, and just want to top up a little.
Most EV owners are very honest and we want to spread a good image of the community, however you will always find people who are not considerate. I would therefore advise that you address the situation upfront in your Airbnb ads. State whether or not you allow charging, and start the conversation with people so that you avoid any possible tension.
It is a new technology that will soon be part of everybody's lives. I would advise to read up on it, get involve and embrace it with open arms, as it will undoubtedly lead you to interesting discussions with future guests.
