[Verizon HTC Droid Incredible 4G LTE] mdmower:
This is actually a tricky question to answer, and I might not be the best qualified, but I'll give my thoughts and impressions which are not necessarily the viewpoints of other CyanogenMod developers.

For the case of features present in CM7 which are not part of CM10+, some of these omissions were design decisions, both by Google and by CM developers. There's a constant battle between reducing clutter and offering enhancements. As some features like UI customization, built-in file manager and audio player, and pull-down tiles gain priority, they tend to replace some of the lesser used features (which may be difficult to implement or maintain) rather than supplement them. The idea here is that packages and mods can always add or replace functionality later.

Clearly, new ideas do need to enter the ecosystem, else the product gets stagnant. The route to getting these features implemented isn't so clear cut though. While there exists an official issue tracking system (JIRA, described below), not all developers pay attention to it. If end users have ideas, there are a few options. Let me start with the don't do this option though: do not post feature requests to CyanogenMod's social networks (e.g. Google+). Seriously, just don't. With that out of the way, the best way to get your voice heard is to put some work into the feature yourself before requesting help. This doesn't necessarily mean coding; it can be design mock-ups for instance. I can say with some certainty that the reason I got to the point of being able to share these releases with you all is that I tore my hair out building up as much of a completed device tree as possible before reaching out to developers working on similar devices (recall the cwm and twrp recovery releases, those were my stepping stones).

Say you have put some work into a new feature and have gone as far as you can into the creative/coding process, where to go with it? MJL99, you've exercised the most obvious route, contact your device's CM maintainer. Depending on the maintainer, this may or may not pan out. Some are receptive (check out h8rift for instance, he actually has an issue tracker), some just want you to be happy with the food in front of you. In my case, I'm still trying to get this device in compliance with a CM policy: Everything-- every peripheral, every wireless feature-- that is supported by stock *must* be supported by CyanogenMod. While I'm receptive to feature requests, I'm simply not going to prioritize them until more of the known issues are resolved. Honestly, I have a feeling this is the case with many other device maintainers as well.

The JIRA project manager is CyanogenMod's new issue tracker. It is still gaining popularity, but developers are supposed to pay attention to these topics. Read up on JIRA in the CyanogenMod wiki.

The next viable route to make a feature request is through IRC. Check out the CyanogenMod related channels on Freenode. Be courteous and demonstrate that you've put thought into the issue.

Failing these options option, your next step is to go through the CyanogenMod github repositories and see who's actively making commits to the repo related to your feature. I can't stress this enough though: if you're going to contact one of these developers, make sure you have put some work into the feature yourself! Realize, these aren't paid, elected officials who must bend to the will of their end users. They have every right to tell you, "no, go away".

In sum, the point I have tried to drive home is that you need to demonstrate a willingness to contribute yourself before many developers will take your feature request seriously. Sometimes, the idea is simple, straightforward, and an obvious inclusion; more often, the logistics take time.

MJ99, as for the specific topics you mentioned: FM Radio is something I'm looking into already to see if our device can support the feature; you will need to seek out mods to extend hardware key options and lock-screen features (these were intentional design decisions by Google and CyanogenMod).