We lack exploration, not even as an engine, but as an option. You can only go to some usual location and look for something there.
I am not sure what you mean with "option", we have engines, you've seen Jake's engine possibilities, you've seen the pseudo3D thing and now there is an example of rpg-maker like engine in the cookbook that runs really, really well, not mentioning Alkions design and my ancient walkabout. But any of these will require insane amount of effort, time and resource. I doubt that we'll have proper exploration until post 1.0.
Thus it's impossible to truly hide something in order for players to search for it or even chance upon.
Yeah, I guess you could hide something via SE. But it has nothing to do with MC (= player himself), since your girls will find it automatically and behind scenes.
Matter of opinion, people manage excellent quests, events in faaaaaaaaaaaaaaaaaaar simpler designs than ours. SM for once... they have insane amount of on map content in a simpler map while many of the request/events do not even deal with st goals at all but add stats/skills/experience/items and etc.
Hiding...
- How about a barely visible button masking itself in the background?
- Or have all but one (or just all) characters from a specific origin?
- Or only after specific day (157)?
- Or to appear after a certain level, stat(s), skill(s) have been reached?
- Or on the full moon?
- Or only on Wednesday?
- Or only when a specific item(s) is equipped?
- Or only after some unique interaction with the character?
- Or SE... they will not find anything if you only add the item to the location after/during a quest/event.
- Or taking a specific place in the Arena ladders.
- Or, or, or, or... conditions are limitless, whatever you want to hide, will be hidden unless they are fulfilled.
Even with the most basic VN tools and a couple of characters, people make awesome games with events, multi-endings, choices and etc. This "one thing is missing because we don't have
"IT", (this one last thing that we need to kick ass) 
" is bs and an excuse. With a bit of imagination and effort, possibilities are already endless.
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I'm not really sure if it possible to add something to tag system at least. We already have all available decent pics in packs, and if it's possible to find more somewhere, it would require a huge amount of time. Same goes for tags, even if we add some new categories, pictures for them are too rare to be widely used.
You're prolly right or at least I hope that you are

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On items front... should we add fields like "battleready" or even a separate slot for items that we want to add to BE. I am sick of the items code, going to take a look at BE for while, see if I now have enough skill to understand it better so interface can be improved and maybe some new options added or at the very least, make the life simpler for me in the future.
Otherwise, maybe I can take a shot at building out own simple BE.