In no particular order:

Fix "utils.c:98:30: warning: logical not is only applied to the left hand
side of comparison" - insifnificant, swapping should be enough.

Request a (min?) height of 80 for the GtkTextView-s, for gtk+3 only.
gtk+2 works fine.

Don't allow Run/Continue without a program or script specified, it's almost
always a mistake, but allow an empty script, even the system null file.
Simplify the startup sequence. Simplify the Program Setup dialog, block OK
if neither program nor script is specified. Update the documentation.

Replace the "Temporary breakpoint on load" with "Break on startup", using
gdb 7.7+ -exec-run --start. Simplify the startup sequence. Place a label
near the checkbox that gdb 7.7 is required. Update the documentation.
Convert the temporary location if any to a regular breakpoint?..

Windows: add "Break on ExitProcess" and "Break on TerminateProcess" to
Debug -> More?.. Useful for stopping at console program exit, since the
console now closes automatically.

Write more friendly documentation. The current one now seems a bit haughty.

Add a setting for the gdb version, along with a "Detect" button? We only
need it for -exec-run --start, the double-escape bug under in the Windows
breakpoint list (fixed between 7.6.1 and 7.9.1) and the var-update bug,
which was fixed at some point. Doesn't seem worth.

Add a (renew the?) PR for the project-before-save signal.

Correct locale from/to utf8 for variables under Windows: utils_get_...()
from Geany should be g_locale_from/to_utf8(). Maybe provide a default Auto
setting which detects utf8-or-locale?

Add a [ ] Pending checkbox in the breakpoints menu? Currently a breakpoint
that succeeds can't be marked as pending for the next child runs.

Create a PR for ui_setup_open_button_callback. It was discussed long time
ago, but ended without a resolution.

"No breakpoints. Hanging." - with a program or script always present, this
should be a per-program option. Also improve the text.

Per-program gdb executable. 3-rd tab "GDB" in the Program Setup dialog. Move
the gdb prefs there, including the bugs. Verify that the registers are
re-queried on gdb change. A few more gdb options, maybe CL options too, for
example --quiet, but only ones that can't be set via script.

set_error -> set_error_literal where the text is static.

Setup Program _Import -> I_mport, the underline is too short now. Add _Help,
call the browser at #set_program.

Add a note in the documentation that the memory offset, count can't be saved
because of variable address/size changes on recompilation. Add a ^(Scope)
command for inspecting memory.

Change the "=li_brary" in the che label to "=li_brary-...", add a TL note
that the "=library-..." text must not be translated, but the underline may
be moved anywhere.

Add a note that "[ ] Show Tooltips" requires restart (does it?..)

GDB has an option to add the command execution times to MI, alter the parser
to ignore them.

Convert the thread exit codes to decimal. Options for decimal/hex/as-is?

Write a Preferences dialog for the global preferences?

wchar_t / L"text" support?

Save sort column #-s?

Check what's new in 7.7 and later. Add --language=C to all commands that
produce variable texts? "--skip-unavailable"? Better support for
catchpoints?

Use the new plugin startup that allows failure, and check for the glade
file?

Per-program options to hide views: Program Terminal, Threads, Memory,
Debug Console, Registers.

Add a ^(Scope) command for (de)activating breakpoint groups and a
on_break_signal() handler: a-h activate, A-H deactivate. Add a single letter
(none, a-h) Group submenu to the breakpoints menu.

Set breakpoint by clicking on the empty space before of a line, where the
markers are shown.

Message "<thread X | Program> received signal Y"?

Try DND-selected-text support for Watches, Inspect?

Try Watch formats or radix.

Mark "Delete all breakpoints, watches ..." with bold if the program or
script name was changed.

Add a second Memory page? (Supporting 2+ regions in a single page seems
confusing and uncomfortable UI.)

Max display length for MI? Should try some very long lines, to see whether
that makes sense. Failed MI must be fully displayed in all cases.

Disassembler read-only editor window using the gdb commands only. Auto open
on assembler location hit. That'll take some work.

Remember 3 lines around the breakpoints and try to apply them as in patch,
in the case that source was modified without the breakpoints loaded. That'll
take work, too.