FPGA that upgrades Amiga 500 custom chipset or allow internet browsing...

[freqmax]

0) MP3-player via mouseport
Can you really transfer fast enough (15 kByte/s) without excessive CPU load through that port? Other than that any DSP + D/A should suffice to accomplish the task. I would recommend parallellport.

1) Webb accelerator
Once you require so much functionality you might as well run the browser on a PC and use a live video switch that will embedd a window from said computer into the Amiga output video stream.

2) Emulator FPGA card
That already exist, it's called FPGA Replay.

3) Custom chipset upgrade
What you suggest would in essence replace the Amiga. So much you might as well use the FPGA Replay.

Reconsider what really is useful.

[freqmax]

At some point the Amiga becomes just a fancy keyboard attachment to something else

[freqmax]

Let's face it, a bog standard 2MB A1200 isn't much fun, they only become usable with a memory expansion card.

I must have been a Houdini with my A500 1MB v1.3 then ..

There's some things that makes the amiga feeling:
 * The physical design - it looks like an Commodore Amiga (design theme)
 * Keyboard layout
 * Motorola 68k compatible instruction set CPU (especially big endian, MOVE etc)
 * Blitter and other raw hardware acceleration
 * OCS, ECS, AGA graphics compatibility
 * Amiga operating system with a matching API

I think as a minimum big endian, and a instruction set that allows direct movement of data like the MOVE instructions without any intermediate steps, hardware acceleration, and an OS that allow direct access with low CPU and memory footprint is needed for the "Amiga feeling". The technology has moved on and one has to take that into account to be relevant. But the concept of making the most for a budget price can still make a difference.

[freqmax]

Maybe you should ask.. What is the most hardware bang for the buck I can accomplish for 700 USD that will make nerds salivate.

Apple did something along the same line for design fanatics..