I don't know about the florescent idea, it should work, but for LED tubes, just get a non-dimmable tube and use a leading or trailing edge dimmer and they will flash and flicker like a (...) no fancy controller needed just a $1 restore rotary dimmer, or you could just run a dimmable LED in series with a florescent starter, I do this with low wattage gls and they flicker and flash in a truly random way, and most last for several seasons of Halloween and an LED should pull enough watts to make it work, I also pull the covers off them so you can see them flash and I stick them in a clear plastic pill bottle tied to the wire so it really looks like something is shorting out...

Make sure you post the video I want to see them when your done, I like Halloween decor as well..   

Well, the problem is, such system will get killed pretty fast:
The inrush current of the non-dimmable LED ballast does wear it out, normally that is designed so it withstand sufficient number of cycles to last reasonably long with normal user switching (usually the order of few Meg cycles). But with the dimmer, such inrush pulse will happen 30..120x per second, so even quite a generous 10Meg cycle (for 1000x cycles per day it would mean 27years life limit imposed by that; so no real limit compare to other effects) life will be eaten within roughly 100 hours.
The same inrush current spikes overload, so wear the dimmer triac as well. Plus the capacitive load makes the dimmer circuit not operating properly, what often means heavy overload of the control part (burning the pot when close to maximum power setting; don't ask, how I know that) Many tend to fail within few hours when treated in such way.

For the rectifying tube problem: In a current limited environment (so behind a choke or resistor) I've never seen any diode to fail. But I've seen many fluorescents to rectify at EOL. So yes, such failure mode is hypothetically possible, but very extremely unlikely to worry about. You would have to do really very poor connection job on the rectifier. And if you are not 100% sure about your skills there (that is no shame at all, don't get me wrong), just use integrated rectifier (the 4 diodes within one component). There whatever of your joints fail, it just can't lead to any input rectification, so your ballast remains safe...
Just the plain LED chain failure behind the rectifier is many orders of magnitude more likely, but those don't lead to rectification either...

So I guess I stick with T12 then.

This spooky thing did bring my mind one onteresting implementation of lighting upgrade. I was in a basement of certain old big apartment complex. The basement had long corridors featuring different kind of service areas and storage spaces and I was on a job searching for telecom room. The lighting in the corridors was upgrade at some point and used led fixtures with each having it's own motion detector (lighting only that particular fixture). The off delay was pretty short, around 30 sec. I stopped at one point to look the blueprints trying to find if Im even close to that place. After a short while I noticed how the lights behind me started to turn off one after another until only two closest of me was on, otherwise it was dark corridor. I can believe that was pretty energy saving setup but I can't say thats really a wise implementation of motion detectors.

I disagree.... i verymuch like the idea of the lights slowly turning off behind me... lol... creepy

I would buy decent looking LED retrofit tubes, gut them and install RGBW WS2812/2811 LED smart strips in them and control them with an Arduino. With the WS2812/2811 LEDs which are individually addressable, you could use an Arduino to control the color of each individual LED. You could program the Arduino to mimick glowing cathodes, mercury starvation, set custom color temp even do color schemes with the "tubes" that wouldn't be possible otherwise.

* A F40T12 and dimmable magnetic ballast.

In either case I'd use one of my christmas-light controllers.
I'm thinking that "candle flicker" mode might make a nice creepy bad-fluorescent look
Have no idea if constantly varying the output level at a relatively speedy rate like that would hurt the ballast,

Did alittle test tonight and...the "candle flicker" mode does infact give a very convincing 'bad fluorescent bulb' look . LOL .
Fine for a short test, whether it'd harm ballast or lamp if left running for multiple hours, I do not know.

(ofcourse depends on the settings you use, you can make it very flickery/annoying or mellow it out very much so it just sorta slowly flickers a bit)