Tabs are used to split a program up into workable chunks.
If I want two programs open, to use 2 serial interfaces for example, then I open 2 copies of the IDE.
Agree. A project (sketch) can have many tabs (files).
Not sure if this is in an area you can or intend to address, but it would be great if instead of
Binary sketch size: 16,814 bytes (of a 32,256 byte maximum)
we could have SRAM utilization as well as flash utilization, e.g. output from avr-size:
AVR Memory Usage
Program: 16814 bytes (51.3% Full)
(.text + .data + .bootloader)
Data: 694 bytes (33.9% Full)
(.data + .bss + .noinit)