the dev would be able to answer the feasibility.
*bing*
- Is there a better/built-in way to cast them other than moving the face down planned ones over and manually subtracting 2 Mana?
Currently, no, as the game does not differentiate between casting a facedown enchantment on something and just moving the card around.
- How does one suppress the reflex to double click for casting/processing one gets from casting other cards? That reveal can be awkward. >.<
That will come with time. However it is certainly possible to put in a little "Are you sure?" window whenever a player double-clicks a face-down enchantment.
- Is there a way to actually attach enchantments to their targets? For now, I can only find drawing a box around them to activate them all, then moving that group. Every. Time. I'm pretty sure I saw group movement without the box in some video or other though, so maybe I'm just missing something.
This is possible via scripting. If cards could be attached to each other, then your first issue could be worked into that as well (pay two mana whenever you attach an enchantment to something else). There are a few things to consider though, like how people put equipment/enchantments on their Mage off to the side of the board.
This has been in the back of my mind as part of a long-term add-more-automation initiative but I don't have a ballpark date for you. Right now I am going after low hanging fruit like resolving Burn tokens automatically.
Convention question:
Usually you know/expect full well that you're facing a nullify/block or defense etc and are deliberately trying to draw that out, so will wait for flip/noflip confirm before proceeding in relevant situations. What if you forget? Just roll back to fix it, ignore rolls, and too bad about any inadvertently revealed information?
The rulebook says that if you illegally flip something like a Block or Nullify, it is destroyed without effect. A bit harsh but the most fair IMO. If you forget to reveal a Block or Nullify then rolling back is a solution, destroying the enchantment without effect is another. Whatever you decide should benefit your opponent, though, as you misplayed.
Usually what I do is the shift + click thing to draw the arrow to show what I am targeting with my spell, then wait for my opponent to say "ok" or reveal in response.
Semi-mechanical follow-up to that:
Also, any user-friendly way to communicate these things with button press chat outputs (like the "is done" ctrl right) or HUD displays or something? With chatbox being active killing the game interface, the whole affair seems incredibly onerous imo.
It is certainly possible to add more text messages to the game. I am not sure that adding additional information in a HUD is possible - I am pretty sure OCTGN only shows cards, markers, and the like on the board. I don't think that even something like floating text is possible. Even if it were possible it would take a good effort to get that HUD to sync between the players (OCTGN automatically syncs the cards/markers/etc for us). Since the chat window is already sync'd it doesn't make much sense to spend time implementing something that already exists, know what I mean?
*bing*
