i have macros for low on mana, spell locked (sleeped, feared, sapped, etc), and when i get aggro on me (for my healing toons). i modeled them after castyeller, my low on mana macro is "/s <<< Low on Mana! >>>". i like the say channel because it stands out and shows a ballon, but it's not as annoying as spamming raid warning or yelling.
anyway, i always have to click these macros, which can cause delays in my healing. i got to thinking that it would be nice if an addon could auto announce those and i thought of castyeller first. it may be outside the scope of the addon, but i would like to see such announces, atleast for low on mana and spell locked (aggro announce would be probably be more difficult since its more situational).
advanced options for such announces would be nice too:
-option for which channel each announce could be directed to (say channel for me, but others might want a different channel)
-mana threshold for low on mana announce
would also be cool if the low on mana announce could check to make sure you don't have any mana pots or innervates ready and suppress itself if so.
just some things i would like to see, although like i said, might be beyond the scope of what you intend castyeller to do.
i have unchecked casting failures and spell misses for my druid, but it seems they still get announced for rebirth (accidentally cast it when it was on cooldown once) and sometimes for hibernate. not sure if it happens with the other druid spells too or not.