Most of these ideas stray very far from the aesthetic the game seeks to create. Adding them would make it feel more like a Saint's Row game. (I.E. what place does horses have in this story or city? They'd be very much out of place...)
I do agree with some of them though.
Here's a few I can think of that I think would fit in perfectly with the game as it is now:
1. GAS MASKS! They have masks, they have tear gas. they shoulda definitely had gas masks. You get hurt by your own tear gas cans...thats stupid. Plus gas masks look cool and they had them on with the exterminator outfits
2. POLICE K-9 ATTACK DOGS! This was their perfect oppurtunity to include K-9s since they already introduced dogs. As long as they don't kill you in 1 bite this would be a great addition to the stale and simplistic police A.I. (sidenote: should be able to have dogs as any character, even in GTA Online)
3. ABILITY TO FLIRT/DATE! This is long overdue. They've included dating and sex in the games, and they have a system in place where you can impress people based on your clothes and car. I just want more options to talk to the NPCs; would love to be able to flirt with people, it'd be like a minigame trying to win them over and get the digits
4. HEADPHONES!! LONG OVERDUE! I WANT TO LISTEN TO MUSIC WHILE IM ON FOOT! This would be especially useful for the PC version if you can stream your own music.
5. CAMERA FLASH! cmon now, this is common sense, and it'd be fairly easy to do. Make the flash like the Xenon lights for cars and you're done.
6. UMBRELLAS! It just makes sense. NPCs should be taking out umbrellas when it starts to rain. And the thought of punching someone carrying an umbrella is just funny to me. Also beating someone with a closed umbrella...that'd be sweeet.
7. AXES! Would be great to be able to use an axe. You'd get it from firetrucks or laying around in the woods and near sheds.
8. BILLIARDS!! Bring back billiards damnit! NOOOBODY wants to play darts! How many Darts video games have you ever heard of? Now, how many Billiards games are out there? See my point?
9. PARASAILING! We got oceans, speed boats, and parachuting. How hard would it be for them to create parasailing as a past-time? Would be a great sport for GTA Online too, since you need someone to operate the boat
10. Last but certainy not least: TRUE CHARACTER SWITCHING! They need to make it so that we can start a killing spree with all characters in the same area and have the ability to switch between them on the fly, like how we can do in the missions.