Over the past two years, I've developed a relatively successful WordPress plugin. It started out as a hobby project, but now I'd like to try and turn it into a business.
About the plugin
What's your take on these options? What avenues of monetization have I missed?
To develop a business, you need to think about it as a business. Most businesses don't have only one product. What you DO have is a happy customer base who have a good relationship with your 'brand.' I would start with that.
You can look at your users. Can you segment them in any way. Are they in particular industries, companies or individuals, in certain geographic areas etc.? You can look for other problems your users have with Wordpress that need solving and that they would be willing to pay for.
Once you have identified this information, you have the basis to build a business. It probably means that you will have to develop other solutions (plugins or other) that people are happy to pay for but the work you have already done is not wasted since you have built a customer base that you can now leverage. This is actually the one of the hardest parts of starting a business so if you can now find a problem to solve for them, I think you will be up and away.
How about using these success stats as reputation. Could you write an eBook for other WordPress developers about developing a product of such quality and demand. I am sure you have some lessons learned and tips/tricks. An eBook version could even link to or include examples from your code, since it is already openly available.
You've identified the possible options very well. I would stay away from the shady stuff, life is short.
The challenge is that there is very little precedence for building significant revenues from a WordPress plugin.
If it were me, I'd try some sort of freemium offering. If you're getting 200 users a day, you might be able to convert 2% of them (4 people) to paying customers. Not a lot of money, but it's something. The hard part is going to be deciding which features should be in which edition.
Be active on forums such as the WordPress Meta and any and all Meetups about WordPress (network). Find out which sites/services are offering a similar type of service, and anaylize their backlinks for further leads.
You can always go more with a B2B model and focus more on marketing to medium/large companies and high-volume WP developers.
You must offer added value to your current users so they find a reason to continue using your service and paying for it. Make sure you keep up with them (wherever they are). I mean, focus on where you're customers are likely to hang out, and you'll find more.
Simultaneously, I'd be hitting any of the great, major WP plugins or tools with an offer to partner. While valuable, your tool seems to need little more oomph to go beyond freemium. You've got your work cut out for you.
You've made an awesome start, but turning the free plugin into a revenue strem may not work well. People get used to free. They don't want to start paying. And, most people are not willing to pay for WordPress plugins, even if they use and love the free ones.
So, it may be hard to monetize the plugin. Here are some ideas:
It would probably be easier to monetize something similar that the users would need. You could market it from within the existing plugin, for example on the admin page. You could develop other plugins, pay someone to develop them, or joint venture with other plugin developers that have great plugins.
Also, is it possible to collect email of the users? If so, you can email them about your other paid plugin(s). You could become an affiliate for other software and email them, if it is allowed in your and WordPress policies.
Regarding SaaS, that could be a good idea. But it would require a greater investment. Also, how would you market it? Would it just be for WordPress users or for anyone with a site?