Multiple uart channels circuit
In terms of elegance, I would say an FPGA. It's relatively straightforward to set one up with loads of UARTs, especially if they're all at the same baud rate etc and you could connect them via local bus or maybe even SPI bus[es]to get the data in with a DMA. However, you have to be sure that your micro can cope with processing 28 channels of serial data at the same time! You'd also need to check the FPGA had enough memory to have half decent buffers as you're looking at a maximum of 315k bytes of data per second if all those UARTs are going full pelt. 

You could even use a NIOS soft core and do it all in one.