Firstly - thanks for trying something different, and it has made for a very interesting start to the game.
Whilst I love this rather tough scenario, with tighter, more expensive slots, high fuel prices and high interst rates to begin with, I'm not actually sure if it will allow new players to enter successfully.
1 - The decision to start at 50% slots allowed me to build up a nice slot bank between 4am and 8am - as I chose my aircraft well. This froze out the ability of competitors to build a profitable schedule - and hastened the demise of competitors very early on.
2 - The slot-a-palooza we have today is permitting high frequency routes (I just launched a x7 daily PEK CAN service using 105 seater aircraft) to be launched with real ease. Competing against this for a new or smaller carrier is next to impossible as the slot costs are high and frequency is key. This can make the stronger carrier stronger and hard to compete for a weaker or new carrier.
3 - Slots a plenty also allows for entry into secondary hubs easier, but the largest cities that dont permit second bases to be made are still secure- making carriers who choose these hubs very safe indeed once older competition drops out of the story.
4 - The restrictions on aircraft comining into the used market (why are there 237 732advs being held back for sale on the used market, but buckets of unwanted 707s available) also hinder new carrier growth -for example - I had a new competitor in PEK, and he chose the CV990 as his aircraft - no chance he could make money, yet if he had 732s available, he could have survived. Having to choose older aircraft ( I have a fleet of 50 or so IL-18s) also results in excessive maintenance costs, which have caught lots of people out.
So for me
1 - permit open access to all cities for second hubs
2 - the used aircraft market needs to recycle unwanted aircraft quickly
3 - slow down the growth of slots, but start at more than 50% (200% should take 10 years to achieve)
4 - keep slot prices high
In summary - this game is following the US model of slots a plenty, demanding frequency operated by small aircraft, rather than the eurasian model of restricted airports and larger aircraft. Considering where the US aviation is in terms of profitability, I think we are in for an interesting game finale. Efficiency is the key in this game.