A user is asking for a share of profit after suggesting a feature

I developed an app and after it's been 1.5 years on the stores, a user wrote an email with a suggestion for a feature. I replied that "yes, thanks for your suggestion, it's cool and I'll implement it in one of the next updates". I added the feature to my TODO list.

Today I got another email from him saying that since the feature is so cool he wants to have a % of the app's profits for his cool suggestion. I don't earn much from the app, and I'm in Russia where that user won't reach me in case of a lawsuit anyway. Still, I replied to him with the following letter:

Hi, I don't earn much on this app anyway.
Still, to avoid any complications I won't implement your idea for legal reasons.
You can sue me or something if I still implement it some time later, but I swear I won't do it.

Sorry, that's common practice in IT industry, from what I know, but I see this for the first time myself (when an app user requests a share of profit after suggesting a feature).

I hope this sounds fair to you,

I think it's completely unfair to ask a % of a profit after submitting a feature request. It costs money and time on my side to implement the feature while I also bare all the risks, and some user hasn't spent any effort or money. Also, the app was successful already before the feature, so a minor feature addition won't bring any significant increase in downloads anyway. So, there is no % to discuss here.

Was my response correct? Was I too harsh? Can there be any complications from this email of mine? Was I maybe too defensive? Should I have just ignored his email?

What do large companies with big products do? Say, if thousands of such people would send such emails to Microsoft about MS Office, Microsoft would quickly run out of features that it could implement without legal complications.

The worst thing he can do now is to write a bogus negative 1-star review but I don't care much for that because there are lots of other (good and bad) reviews.

This all seems obvious, but I just wanted to make sure there are no non-obvious legal caveats here just to be more educated for similar situations in the future.

Your response certainly angered him as you won't be implementing his feature and you won't give him anything in return - you should have done both !

If the feature is great, implement it, and if you implement it give him something, like free updates and credits.

Asking for a percentage on sales is of course out of place, and unless he managed to patent or copyright that feature before he submitted it to you, there are zero legal consequences.

Big companies certainly aren't as flexible as small/individual companies when it comes to adding requested features.

Don't worry - there is almost no chance that he could do something against you.
On your place, I would even implement it, without bad conscience. In the majority of cases, the ideas itself are useless - until someone realizes them. He could already be happy that YOU implement a nice feature HE WOULD LIKE TO HAVE. Now, he can be angry only against himself, because at the end, he will not have the possibility to use this feature.

I am very hard, I know - but his approach is frankly blameworthy. He could say directly: "If you agree to share you revenues, I have a nice feature that will boost your sales. " Than OK. But telling first: "It woud be nice you inlude this feature to your program. " and then come later begging for % of the benefit is really not serious...

So don't worry, don't excuse yourself. This kind of blackmailing doesn't deserves your time...