Guild perks (guild tabs) were introduced in Cataclysm and the ability for trial-accounts to join guilds was removed long before that.
And Pet Battles are completely different from what is currently being discussed. It's a feature of its own while the heirloom tab isn't.
I have said this many times already; it has been stated that the heirloom tab will work similarly to the mount and pet tabs.
Your examples are completely different from the currently discussed feature. If Blizzard was to, for the sake of argument, add the ability for you to challenge others in various minigames; then I would agree with it being a fifty-fifty chance of F2Ps getting access to that feature. That's because minigames, unlike the heirloom tab, would be an independent feature.
Now let's return to the heirloom tab. It is not an indepent feature, it is based off the mount and pet tabs. This means Blizzard has just revamped the mount and pet tabs to also offer you the ability to save heirlooms across WoW-accounts under the same Battle.net-account. We can therefore safely assume that it will be accessible by F2Ps since the mount and pet tabs also are.