'Let's Play' is the concept of playing and recording video game footage for the purpose of providing entertaining or informative content. It's synonymous with platforms such as YouTube and Twitch, but it's humble beginnings were actually on the Something Awful forum and in the form of a collection of screenshots. Before capture cards people would setup video cameras and record their screens. 'Let's Play' has been around for about a decade.
Considering the biggest change in the current PlayStation's functionality is the share button and the ability to record, edit and upload footage to social networks as well as Stream, it's a good assumption that Sony could want to cut out the middle-man and provide a complete platform via a 'Let's Play' app. This could be a good and bad thing. Logistically, it could be a lot simpler and faster to get your 'Let's Play' footage up on a channel (that channel being hosted on Sony's new service). It could also mean that from a license point of view, it would be a lot safer to upload and monetise footage, because Sony (as the arbiter of their service) could potentially give an across-the-board permission-slip, meaning videos wouldn't be being claimed.
Despite the change of the digital landscape when it comes to YouTube and the benefits of allowing 'Let's Play's' from a marketing perspective, copyright claims still come in thick and fast from some companies and so this could be quite appealing to some people. However, established YouTube channels and Twitch streamers who rely on PS4 content would be very unwilling to move platforms and would almost certainly take a hit to their subscriber count. Sony could make the decision very easy for people though by updating the PS4 and permanently turning on HDCP - rendering capture cards useless and forcing players to use their own service. YouTube takes about 45% of revenue from ad sales, but Sony could take less than this to soften the blow and entice users over to their platform, or they could just be dicks and take more - the former would probably be ideal from a marketing perspective. YouTube uploads could be allowed by Sony (after they take a cut, similar to Nintendo's current programme).
Personally I think it's a terrible idea, especially since whilst there may be a lot of console exclusives out at the time of the release of this service, many larger YouTubers who use mixed content could just boycott the PS4/5 and use other platforms (such as PC which generally has the most exclusivity). Sure there will be big business for some YouTubers new and old, but moving a large audience from one service to another won't be easy. I don't actually think Sony would do this personally, and instead I think it's much more likely that they want to improve their existing tools to allow content creators to avoid editing on their computers, and to stop using capture cards altogther. Being able to upload your own images, animations, titles and use key-frames on the PlayStation (especially using a cloud service) would be a nice feature, especially since the basic object properties and key-frame options is all that a lot of 'Let's Players' need - large channels included. Not everyone has a computer with decent editing facilities anyway, plus anything that saves on editing time is always good - although sometimes the biggest time saver for me is flexibility, not simplicity (yeah I'm look at you native Apple apps).
Now onto the legal element of this and what Sony's claim could mean for everyone else who uses the term 'Let's Play'. For a start, no one is going to stop you from recording game footage generally - don't worry about that. The term 'Let's Play' has been used for so long that Sony would have a hard time appealing this one. Even if they did get the trademark then I don't think they would aggressively take down all existing videos with 'Let's Play' in the title - I think this would be a pretty disastrous thing from a PR point of view. Many people don't use the term anyway, but those that do could potentially have to stop branding their content in such a way to avoid Sony making a claim in the future. One of the biggest games media companies on YouTube - Rooster Teeth - do have a channel called 'Let's Play' - who I'm sure have many many lawyers ready to defend their right to use it as a brand. -oP