I usually play career mode, but often find the contracts (including all the add-on packs) shallow and boring, not to mention unrealistic. There is no storyline, and I cannot do obvious side-missions because cash is not paid out until after I finish a mission (at which point I don't need the money anymore). As I compared my missions to those of NASA, I suddenly got an idea that I think could drastically improve the fun of career mode.
Currently, KSP contracts are given in accordance with where the player is holding exploration-wise and part-wise. They have a modest advance payment (mostly cash, sometimes reputation) and a substantial reward (mostly cash, some rep, and sometimes a little or a lot of science) upon completion. There is also a penalty which approximately retracts the advance, while giving negative reputation. Part-testing makes the part available as long as the contract is active. Unintended achievements give rewards too. The most important milestones do not have a deadline.
However, real-life NASA missions usually go like this: NASA is paid a very large amount to achieve far unprecedented exploration, and for which the technology (parts) does not exist. There is no reward for completion other than reputation. And the penalty for non-completion of a project (i.e. congress cancels it) is just retraction of the funds set aside for it. A new part has to be developed before it can be used. Unintended achievements (like anomalies or mission extensions) are in the news (i.e. reputation and possibly science), but do not result in substantial payouts (only maintenance expenses covered). The most important milestones have a very short deadline.
I therefore propose a mod that results in the user being given long term goals early on, e.g. EVA in low Kerbin orbit, Plant a flag on the Mun, Orbit Jool, Test RoveMax Model S2 on the surface of Duna, Place a satelite in synchronous orbit above the Duna face, etc. The player then has to use the given money to reach the goal by proper resource management: He or she will need to decide on spending money on development (i.e. unlocking parts), upgrading KSC, or on side-missions (that he/she will have to decide on) to gather enough science to unlock the tech tree for the desired part(s). All this in order to complete the accepted mission before the deadline. There will be no steady cash flow from completing trivial missions, only from accepting additional long term goals – which all bring new deadlines. Failure has a severe reputation penalty, and most importantly the retraction of the full advance amount. So if the player has already spent the money, it may cause bankruptcy. Non-contract achievements (world-firsts etc.) only pay science and/or reputation, but no cash.