Enhance in-built Facebook and Twitter functionality: I am not going to argue that the native functionality should expand to the point where 3rd party apps are not needed, but some examples of functionality that ought to be there to complete the native Meexperience:
Like-ing a comment someone makes on my Facebook update. It is related to Meso this should be part of the native experience.
Make Facebook chat be able to send offline messages (today, you can only do Facebook chat with someone who is online), and expand it to group chats/messages. I argue this is native experience mostly because Facebook chat is already native, and the Facebook app does not support these two features. If the app did support these, I would be ok if the native experience did not do these things.
Seeing the tweet to which someone replies. Today, I get a notification when someone replies to me or mentions me, but I cannot see what that tweet was in response to. I have to fire up one of my Twitter apps and see the original tweet. I am not saying I should be able to see the entire conversation, but I should be able to see at least the previous tweet to get context.
Add notification when someone natively retweets my tweet. Again, I believe this is related to Meso it should be part of the native experience.
Native screenshot capability: I love to show off what I see on my phone. Sometimes it is something unique, sometimes it is something cool. As an enthusiast, I may even want to put screenshots in my blog posts to illustrate my points. Windows Phone does not support, for no explainable reasons too, the ability to capture screens on the phone. Yes, there is a way to get it done via a homebrew app but to sideload that app, you have to have a developer-unlocked phone. Developer-unlocking is not a common task, and certainly not free ($99 to have a developer account, and $9 via the ChevronWP7 tool), so it would be nice if Windows Phone could just natively do it, like iOS has supported for the longest time, and how Android is going to support it with Android 4.0.
Allow full-size photo auto upload: Windows Phone was the first OS to have functionality to silently upload your camera roll to SkyDrive for an automatic backup. However, it is crippled because it reduces the photo to a very low resolution before uploading. I can understand there could be concerns about data usage, but I am also certain that as a software company Microsoft could come up with clever ways to get it done. Things like settings for uploading only when connected to WiFi, or uploading a low-resolution copy immediately and then queuing up the high-resolution copy to overwrite the originally uploaded picture later, are possible elegant solutions to the problem.
Include videos in auto-upload: Videos are not auto-uploaded to SkyDrive, period. This should change. We are increasingly taking a lot more long photoson our phones and these video clips are extremely valuable memories and should be backed up just like photos are. If space on SkyDrive is an issue, there are solutions possible like making it possible to buy more storage, or limiting the uploaded videos to the last 100 or up to 10GB or such. Again, nothing that a mighty software company like Microsoft cannot think of, to resolve the issue.