Quite a lot of RS232 is now transported over USB, and so is often not RS232 signal levels where it is used, but 5V or 3.3V. The signals from a USB-UART might be buried in a PCB. So it might not be as easy to see which signals are used as it was when looking at an RS232 cable.
The move to USB, away from RS232, or a 'TTL' signal level of RS232, on the host PC caused a lot of RS232 devices and applications to move to USB. However, the RS232 signals are still supported.
(USB sockets are more compact than RS232, probably cheaper, USB signal levels are more 'PC friendly', USB was faster from the start, and supported many different applications over a common socket and cable system, with the application complexity in software rather than hardware. So it was reasonable for PC manufacturers to move to USB in preference to a plethora of different communication standards and sockets)
FTDI have been supplying USB-UARTs for many years which support several levels of RS232-derived signals. A 'basic' UART supports RTS (Request to Send) and CTS (Clear To Send), and more complex devices supporting RTS, CTS, DTR, DSR, DCD and RI.
Many Arduino's, connected to a host PC via a USB-UART, still use the DTR signal (Data Terminal Ready) to enable the host PC to force a RESET of the Arduino's microcontroller. The DTR signal is brought out from the FTDI USB-UART and connected to the microcontrollers RESET pin.
Host operating systems' serial-over-USB drivers still support 'out-of-band signalling' using those legacy RS232 signals. So the host can open the USB device as a serial stream, then use
ioctl on that stream to manipulate the legacy RS232 signals.
Microchips MCP2200 USB-UART supports RTS and CTS.
Prolific offer the PL2303TA a Tx/Rx only device, but also the PL2303SA supporting RTS, CTS, DTR, DSR, DCD, and RI.
Though it is circumstantial evidence, there are several manufacturers supporting more than Rx and Tx, and having been doing for several years. So it is reasonable to assume their are uses for more than Tx/Rx. However, because the transport is USB, and not RS232 cables, plugs and sockets, it might be hard to see specific evidence.