I can't think offhand what you would run to control an espresso machine that would require more than 256 Kb of program memory. The architecture (Harvard) does not allow code to be loaded from external devices, such as SD cards.
However people are making quite complex things, like quadcopters, and robots, using quite small amounts of program memory.
If you simply can't fit your code into 256 Kb, you might look at another processor. The Arduino Due for example has 512 Kb of program memory.
Bear in mind that early PCs (eg. Apple, Apple Mac) shipped with less than 256 Kb of memory.
From Wikipedia:
IBM sold the first IBM PCs in configurations with 16 or 64 kB of RAM preinstalled using either nine or thirty-six 16-kilobit DRAM chips. ... After the IBM XT shipped, the IBM PC motherboard was configured more like the XTs motherboard with 8 narrower slots, as well as the same RAM configuration as the IBM XT. ( 64 kB in one bank, expandable to 256kB by populating the other 3 banks ).
It's hard to believe that one dedicated device (a coffee machine) would need more memory than you got on the original IBM PC.