I think you should feel free to make anything you want - whether it will be used by other people will be a different story. Casual friendly gamers will probably not bother with these, pardon my language, "screw the opponent" expansions (and there are also already a few official ones that does this).
I'm not sure about the point of issuing even a fan-made expansion that simply plagiarises from another. For example, my next attempt might be
Manor House. I'll issue two tiles that depict Manor Houses. When these are laid on a city it will increase the citys value by one point when completed (because the lord of the manor resides in that city). However, if not completed, the city will score nothing. The artwork will be very nice... but does it really warrant an expansion... or am I simply stealing from Cathedrals? I'm not including any Tavern on a Loch tiles, but is this really a necessary expansion?
All I am saying is that
The Gallows would be the Princess in a different form. Yes, there is no Dragon, Fairy or Magic portal to worry about, which might be a very good reason in itself for doing it. I don't play with P&D, but I'd love a tile or two that do exactly what the Princess does, without the full expansion being in there.
The question you should be asking is, why do you want to make this? If it is for yourself and for your own enjoyment, then by all means go ahead. Sharing it with others would only increase the sense of satisfaction, but you don't need that in the first place because your original goal was to enjoy making it.
There's nothing wrong with doing it for any other reasons (like hoping HiG or RGG will use your idea and make it into an expansion, or to be popular with this or that crowd, or to make the most small expansions, or whatever), I suppose, but you might be setting yourself up for some (maybe major) disappointment.
My goal is to make expansions that I would enjoy using AND what others might enjoy using, without complicated set up times. Expansions with little preparation work are much easier, i'm sure you'll agree. This is why I like Kevin Graham's
Trading Posts and why this variant gets used so much in our games. Lets face it, having RGG or HiG release officially is a long shot (that's a seperate discussion of course). I would get satisfaction when I use an expansion it in my gaming groups games and they say something like, "I like that expansion", or someting similar! I also enjoy working on the rule sets, and the 'what if' questions, but there is no point or satisfaction if the expansion itself is not original. All the questions have already been answered!
In the case of
Jousting Tournament,
Invasion of Catharism,
Orders of Chivalry and
In The Stocks there are mechanics operating that are useful and they haven't been done before (AFAIK). They are original. IMO, originality is what makes for a
great expansion and a fulfilling time creating the rules!
As I am also issuing expansions with CC branding. I would like to think that expansions that include different mechanics are indeed original... not just a CC rip-off of another official or even 'fan-made' expansion. I want them to be high quality, original and simply good expansions that people would enjoy adding to the mix and that perform something that is 'needed' or fits the theme well.
I've been churning out the expansions I have been churning out, because those are the tiles I want to play with and I have fun making them. I think that's reward enough for me.
The expansions currently in development at CC are mostly good ones. The
Forests expansion fits the theme nicely.
Treasure Hunt is highly original (and I might add, one of the best for originality) and
An Apple a Day has the makings of yet another good idea. The Authors of CC are fulfilling different 'needs'. I just don't want to plagiarise another's idea in the way that
The Gallows might end up doing!
