А посему возникает вопрос: можно ли в принципе преобразовать адрес указателя в unsigned int и обратно?

7.18.1.4 Integer types capable of holding object pointers
1 The following type designates a signed integer type with the property that any valid
pointer to void can be converted to this type, then converted back to pointer to void,
and the result will compare equal to the original pointer:
intptr_t
The following type designates an unsigned integer type with the property that any valid
pointer to void can be converted to this type, then converted back to pointer to void,
and the result will compare equal to the original pointer:
uintptr_t
These types are optional.

Не уверен

For example, in an Intel 8086, as well as in later processors running 16-bit code, a far pointer has two parts: a 16-bit segment value and a 16-bit offset value. A linear address is obtained by shifting the binary segment value four times to the left, and then adding the offset value. Hence the effective address is 20 bits (actually 21-bit, which led to the address wraparound and the Gate A20). There can be up to 4096 different segment-offset address pairs pointing to one physical address. To compare two far pointers, they must first be converted (normalized) to their 20-bit linear representation.

Да и еще не так давно почившие 16-битные x86 приложения, имевшие 16-битный int и 32-битный far pointer:

есть стандартная функция ioctl (функция области ядра в Linux).
...
Но проблема в том, что прототип функции таков, что функция может принимать только unsigned int значение.

#include <sys/ioctl.h>

int ioctl(int d, int request, ...);
Description
...
The third argument is an untyped pointer to memory.

real@ECSE2:/media/U2/real/o/avrprg/avreal/trunk/common$ grep -n ioctl lpt.cpp
lpt.cpp:339: claimed = ioctl(fd, PPCLAIM) == 0;
lpt.cpp:352: if (claimed && ioctl(fd, PPRELEASE)) {
lpt.cpp:368: ioctl(fd, PPRDATA, &value);
lpt.cpp:371: ioctl(fd, PPRSTATUS, &value);
lpt.cpp:374: ioctl(fd, PPRCONTROL, &value);
lpt.cpp:387: ioctl(fd, PPWDATA, &tmp);
lpt.cpp:392: ioctl(fd, PPWCONTROL, &tmp);
lpt.cpp:401: ioctl(fd, PPWDATA, pbuf++);
real@ECSE2:/media/U2/real/o/avrprg/avreal/trunk/common$

имевшие 16-битный int и 32-битный far pointer

для получения 32-битного указателя требовалось ключевое сово far (расширение компилятора а не стандарт).

6.3.2.3 Pointers
3 An integer constant expression with the value 0, or such an expression cast to type
void *, is called a null pointer constant.
...
5 An integer may be converted to any pointer type. Except as previously specified, the
result is implementation-defined, might not be correctly aligned, might not point to an
entity of the referenced type, and might be a trap representation.

6 Any pointer type may be converted to an integer type. Except as previously specified, the
result is implementation-defined. If the result cannot be represented in the integer type,
the behavior is undefined. The result need not be in the range of values of any integer
type.

Насколько я помню DOS и BC3.1, для получения 32-битного указателя требовалось ключевое сово far (расширение компилятора а не стандарт).
Для модели памяти типа LAGE все указатели были типа far pointer (BC3.1),